The movie opens with a warning: "The performers in this movie are professionals. Please do not attempt to perform these activities at home. If you attempt to drink this much, you will die."
It opens with a man and another man engaged in a game of quarters. The other man tells him that he's tired of losing all his money to him and that this is a winner take all competition. This man's name is Jan Wolfhouse. He manages to successfully flip the coin into the very narrow flower vase full of beer. The other man - Jan's father, drinks the beer down without fail. Jan's brother Todd shows up and their father is talking about how he's berating Jan in a friendly beer drinking competition. Todd informs the both of them that everyone is waiting. It's then revealed that everyone is at a funeral for the patriarch of the family - Johan Wolfhouse. Johan is in the hospital hooked up to a machine. He gives his own eulogy via a pre videotape where he gives his final wishes while downing a beer for each one of them. One was for his mother who he always knew would outlive him, the other is for his grandsons Todd and Jan, and for them to take good care of the family restaurant. The final one is to himself. He then entrusts Jan and Todd with his most prized possession - a German doll wearing leiderhosen that he calls "Bobo". At the end of the video, Johan pulls his own cord and he falls over and dies.
Later that day, Johan's mother - Great Gam Gam is telling Jan and Todd what to do with Johan's remains. It's then revealed that they are to go to Munich, Germany during a special festival where they are to place Johan's ashes among the remains of their elders. That special festival happens to be Oktoberfest. At Oktoberfest, they are to meet a man who is named Mr. Schniedelwichsen, who is to take them to the family resting place where they are to place Johan's remains with the remains of their elders.
At Oktoberfest, Jan and Todd are drinking quite heavily and are becoming friendly with the other tourists who are in town for the festivities. As they sing the beloved drinking songs of their country, Jan and Todd somehow manage to offend the entire Oktoberfest community with a rendition of "99 Bottles Of Beer On The Wall". As they manage to escape the chaos that ensues, which they themselves had caused, and set off a Rube Goldberg style chain of events that causes the entire tent to collapse, they finally meet their contact that Great Gam Gam had managed to hook them up with. He then takes them from the chaos of Oktoberfest to an underground layer. That layer happens to be the home of a secret competition called "Beerfest".
As Jan and Todd marvel at the competition that's called Beerfest, they are stunned to learn that there is an actual competition involving the drinking games they love - quarters, beer pong, upside down chug, and so on and so forth. It's later revealed that there is no USA team - they're laughably unqualified among international drinking teams because as comes with heavy drinking and Americans so does some heavy fighting. As the competition ends, the German team manages to defeat the Irish team with a game called "Das Boot" - where the team drinks with a huge cup that's shaped like a shoe. The game ends, Jan and Todd cheer on the German team. It's then learned that Jan and Todd share a common ancestry with the German team. But they are not amused as the German Wolfhause squad tells the Jan and Todd that Johan had stolen a beer recipe that was regarded as the best beer recipe that's ever come out of Germany. Jan and Todd challenge their German relatives to a drinking contest only to be humiliated. They're then greeted by the German patriarch of the Wolfhause family who then proceeds to give Johan the proper memorial that they feel he deserves (hint: it's not flattering). They also refer to Great Gam Gam as a prostitute. But Baron Wolfhouse reveals he's the first born, not Johan, and orders the guy who brought them to Beerfest killed. Jan and Todd are then humiliated and knocked out.
Back at home, Jan and Todd are in denial about Great Gam Gam being a prostitute. They then decide that they're going to honor her honor and their late grandfather's honor. They are going to train for an entire year and go back to Germany where they are going to lay the smack down on the German team. They decide that they're going to get the best beer gamers, the fastest chuggers and they're going to give the German team a run for their money in the next Beerfest.
The first one they set about finding is a guy they simply call "Landfill". Real name is Phil Krundel. Landfill rightfully earned the nickname because he is essentially a human garbage disposal and can eat and drink anything and hold his weight appropriately. They first find Landfill at the county fair's hot dog eating contest, where he is dominating the competition. In his past, Landfill was involved in an infamous incident from the brewery (involving him guzzling beers that came off the assembly line) that he was working in that got him fired, arrested, and had him spent some time in jail where he found religion and became a changed man. Landfill tells Jan and Todd that he would give it all up if it meant reclaiming his former glory. Jan and Todd explain to him that this is his opportunity and he's ecstatic.
The next member of the team that they find is Dr. Charles Finklestein, aka Fink. They meet Fink in the lab that he's working in. Landfill has a "get a load of this guy" moment as Fink, an acclaimed scientist and devout Jewish man, is seen collecting the male fluid specimens from a toad. Todd assures Landfill that Fink can beat the boot because he has studied everything about everything, including beer. Fink has two Ph.D's and a nice house with a two car garage. Fink doesn't believe Jan and Todd until they explain that he will be competing against the German team. He then tells the three of them that they've got 15 minutes to explain more.
The final member of the team is Barry Badrinath. Barry and Todd had a fallout in college when Barry had a sexual affair with the woman who Todd would later go on to marry. Todd has held a grudge against Barry ever since. But Barry has fallen on hard times. His pimp won't cut him a bigger paycheck and he's living underneath a bridge with a bunch of other like-minded individuals. Jan assures the group that Barry is the best beer gamer that there ever was, but Barry is having a hard time proving the opposite. Back at the family restaurant, called "Schnitzengiggle", the guys are trying to decide who to get in place of Barry, but suggestion after suggestion proves to the group that they can't anyone who's worthy enough to fill his shoes. Barry enters and proves he is worthy of competing in Beerfest. He then stuns Jan, Todd, Fink, and Landfill by scoring perfect scores on any game he comes in contact with. He claims it's because he's better when he's drunk - that's enough to convince everybody that he's worthy of joining the team.
The next day Jan and Todd present the team with their own training facility. They get a keg of beer and give the team a pep talk about how the next year is going to be tougher than anything they've ever experienced in their entire life - they're going to drink beer, and a lot of it. And if anyone isn't up to the task, they can walk out that door. It's then revealed that Barry can't play beer pong. They then proceed to drink extremely heavily and it's revealed what happened as time went on. The next morning Landfill nearly dies of asphyxiation, while Barry wakes up in the middle of nowhere, completely naked, next to a deer and screaming "Oh god not again!!!". With half a keg left over from the wild night before, Jan and Todd decide that they need some serious help if they're going to beat the Germans. They go to Great Gam Gam's house where she has enlisted the help of an obese caretaker named Cherry to help her now that Johan is gone. They then consult Great Gam Gam about why the Germans are amazing beer drinkers. She assures them it's because they drink the urine of a ram, because if you can drink that, you can drink almost anything. Barry comes to the revelation that Great Gam Gam just might be in fact a prostitute because of the not so subtle clues that she was giving during their visit. The guys then set about acquiring the substance and trying it for themselves. While on a rooftop, Fink decides that this isn't the way to go and that they should go about mixing it up with some random people rather than the "traditional method".
The first party they go to is a wild teenage party. The party stops when they enter until Landfill grabs two large beers and chugs them down, he announces that they're the Party Brigade and that they're there to play some drinking games. They do so. Fink tries something called a "strikeout" - where you take a hit, chug your beer, do a shot and then blow out the smoke. He is knocked out almost instantly. Elsewhere in the party Barry and Todd are getting ready to box each other dressed as a bride and groom while the cops are called. Fink is wrapped in cellophane atop a set of monkey bars and cannot escape when the cops arrive.
Now with 8 months to go, while practicing drinking games, Fink discovers the problem with the boot and has the guys gather around to show the problem. He gets into a fight with Landfill and knocks Bobo to the ground. But they discover something inside Bobo - it's a beer recipe. The one that claims to be the best beer in all of Germany, proving the claims about Johan and Great Gam Gam right. Another two months pass and the finished brew is completed and the guys have a toast for Johan. Drinking the beer they have just brewed proves to be a religious revelation for the guys and they think it's the greatest thing since sliced bread.
Four months to go. The guys are out at the bar having some fun playing a card game called "asshole", Barry drinks too much and becomes his alternate persona. Jan shows off the awesome bottle that he created for the house brew, now called "Schnitzengiggle Ale". Barry then picks up what he thinks is an incredibly attractive woman and they head back home for a night of foreplay. The morning however, it reveals that he actually picked up Cherry - Great Gam Gam's overweight assistant and the things that happened are not exactly what he pictured in his head. Barry then reassures the audience that while he was drunk, he knew what was going on the whole time.
Less than two months remain until Team USA heads to Germany. At the restaurant - Schnitzengiggle, it turns out the beer they brewed is a hit and is flying off the shelves and attracting record crowds. So much that a bottle was sent to the German team. Baron Wolfhouse discovers this and sends his team to Colorado where they humiliate the guys at their own restaurant. As they try to think of a name for the operation, Baron tells his team that it's not about names. It's about reclaiming the family heritage. They then challenge the guys to a winner-take-all beer pong tournament for the family recipe and 500,000 Euros. At first they deny the challenge, saying they'll make more money selling the beer than they ever would if they take the money being offered. Todd then accepts the challenge, with Barry as his partner but Barry gets in a fight with Jan because beer pong is the one game he just won't play. He then leaves. The German team then humiliates Jan and Todd by destroying multiple items in the restaurant.
The next day sets off a chain of events that has Jan and Todd nearly calling the whole thing off. Fink reveals that he got fired from the lab due to slipping performance, and accidentally created a mutated race of monkey - frog hybrid animals. The German team files a fake report on live television against Schnitzengiggle that has health inspectors nearly condemning the place and reservations being cancelled left and right. Landfill comes in visibly upset because his wife couldn't take the lies and the heavy drinking and took the kids to her mothers'. Jan, Todd, and Fink are stunned to learn that Landfill has kids. While having one last brew in the back, and recalling the good times, Landfill discovers something suspicious happening. Turns out Cherry is a spy that was hired by the German team to steal the recipe back. Cherry copies it off the computer and she and Landfill get in a fight, and Cherry ultimately knocks Landfill into a vat of unfinished brew.
Landfill attempts to escape by drinking his way out. Unfortunately he drowns and is discovered by Jan. Jan, Todd, and the gang are devastated by the incident and consider packing the whole thing in.Todd decides that he's had enough and that Team USA is done. They're packing it in - Schniztengiggle, the beer, their hopes and dreams of conquering the German team. While at Landfill's funeral, Fink gives a tear-and-beer filled eulogy, while Barry accidentally knocks Landfill out of the casket while being confronted by his incredibly angry wife, who was horrified by the truth surrounding the events leading up to Landfill's death.
During the reception, the reunited team wonders what they're going to do next. They're then confronted by Great Gam Gam who reveals the truth about the family. That she was in fact a German Prostitute. That Baron's father Ludwig had an affair with her and she gave birth to Johan, and that he, not Baron was the real first born Wolfhause. And the Von Wolfhausen Family Brewery belongs to Jan and Todd - not Baron and his sons Otto and Rolf. When the town found out about Ludwig's affair, they had Johan and Great Gam Gam tarred and feathered and run out of town. Great Gam Gam then tells Team USA that it's their destiny to go to Munich to defeat the German team, that the family heritage and the real truth about the Von Wolfhausen family must be reclaimed. Barry reveals to the group the exact incident that rendered him unable to play pong. He was in Thailand playing, and got beat up, and somebody shoved a ping pong paddle up his ass. Great Gam Gam tells Barry that, as a fellow prostitute, she's had all kinds of things shoved in her ass, but she got over it, and so will Barry. As they ponder who to get to replace Landfill, Landfill's identical twin brother Gil shows up and wants to join the team. He proves he's every bit as good if not better than Landfill.
It's now time for Team USA to head to Germany to face their destiny. As they wander around Munich, Jan and Todd actually forget exactly where the competition is. Fink remembers some research that he did back in college and got published in Maxim magazine. It's called "drunken recall". Since Todd was the drunker one at the time, the guys proceed to get Todd really drunk. He does and immediately remembers everything that they needed to do to get to where they're going. They're at first denied entry until they try the old Trojan horse trick and disguise themselves as a keg. At first they're denied the ability to play until the crowd demands that they are allowed to do so.
Team USA and Team Germany have no problems eliminating the competition that they face. They then ultimately face each other in the final round. The first game is beer pong. Otto brings up a technicality that Todd has not competed in any event. They're nearly disqualified until both Todd and Barry announce that they'll be competing in the challenge. Barry and Todd are on the losing end of the match it appears until Barry takes the proverbial bullet and sends the ball flying into the cup. Barry and Todd then reconcile their differences over the past incident involving Todd's wife. Team USA then makes a comeback. The next games are Thumper and Turbo Quarters, and Team USA has no problems in those games. But then it comes down to a tie which means that they go to sudden death and drink from Das Boot.
In the bathroom, Fink discovers exactly what they need to do to beat Das Boot. It's because when you drink it, it forms a bubble. All they need to do is when the bubble comes, turn the boot. In the final round, they have Gil as the anchor, but while the competition is going on, Cherry reveals that she was the one who killed Landfill, causing Gil to fail. Team USA is laughed at until Jan challenges a double or nothing final elimination round. Ten boots, ten players. Winner take all. If Team USA wins, the winner gets control of the Von Wolfhausen Family Brewery. If Team Germany wins, the winner gets control of the recipe. Cherry laughs at them, telling them it's a moot point because Cherry had stolen the recipe off Fink's computer. Baron laughs at Team USA and has them nearly kicked out of the arena. Jan proves that they're the real heirs to the brewery by showing Todd next to the portrait of Ludwig Van Wolfhausen. The Canadian team remarks that they look remarkably similar. Fink reveals that's not the family recipe they really want. In fact, it's a recipe for an experimental low carb strawberry brew called "She Hulk". Baron then has Cherry taken away and killed. Gil then mocks the German team telling them "we're not that drunk". The audience watching starts joining in on the chant.
It's time for the final match. The team gives a pep talk like you see in sports movies. Fink instructs the team to do exactly as he discovered to beat the boot. Then before the match, during some trash talk, Otto knocks Fink's yarmulke off, and that angers him to the point where Jan decides to make Fink the anchorman over Gil. It's time for the match, the referee tells them not a drop can be spilled. Fink manages to beat the German team by drinking furiously from Das Boot. It all comes down to a final drop from the Germans that spills. That makes Team USA champions and they get control of the brewery.
Cut to several months later. The guys are in Amsterdam for some much needed R&R as they find running one of the biggest breweries in Germany isn't easy. After cruising the red light district, they get lost on the way back to their hotel. As they wonder down the alley, they notice a familiar face. It's Willie Nelson. Willie tells Team USA that he's competing in a super secret international pot smoking competition and that his partners Cheech & Chong chickened out on him. He then invites the guys the guys to join them as his teammates. The movie ends with a teaser for the sequel "Potfest".