When Tommy bends the car door back into position at the gas station, it is visibly dented and crumpled along the edge. Immediately after, Richard goes to open the door, it falls to the ground, and is in pristine condition.
While in Zalinsky's Board Room with the TV crew, Tommy gets Zalinsky to give his "I make car parts" line. As Zalinsky starts, he opens his shirt and undoes his tie, next shot his tie and shirt button are closed, then the next shot they are open again.
While waiting to depart, we see a shot of Tommy and Richard's plane waiting at the gate, and it's clearly a two-deck 747. Later, there is an exterior shot of the plane in flight and it's another type of plane, with only a single deck.
When Richard is telling Tommy about his 1967 Plymouth GTX he says "I dropped in a 440 Magnum with a six-pack" (3x2v carburetors). But when the hood comes open it has a 440 Magnum with 1x4v carburetor - the original engine on this vehicle.
When Tommy, his father, and the executives are in the brake pad division and Tommy is doing "Kung-Fu" with the moving hooks, his father catches him and tells him to come on. As soon as Tommy takes a step toward his father, the hooks stop moving, but clearly no one turned them off.
During the last scene on Tommy's boat, there is no rope connected to the pulley wheel at the end of the boom of his sailboat. In the next shot when he sails away, there is a rope attached to it (this is necessary to be able to sail).
In the scene where Tommy wrecks and lights the toy car model on fire, the front axle and wheels are missing from the table in some shots, and the blue car is set on the table in different spots in some shots as well.
Richard hits Tommy in the face with a 2x4 when they get into a fight. This board was nowhere in sight in the long shot of them getting out of the car, and not enough time passes between shots for Richard to have run off, found it, and returned.
In the airplane lavatory the bottom half of Tommy's tie gets in the blue chemical liquid of the toilet, which is permanent. In the following scene in downtown Chicago the tie is like new with no hint of blue chemical stain.
Richard hits Tommy Boy across the side of his face with a board. It is revealed, during the lunch scene at The Cluck Bucket, that this left a huge bruise on Tommy Boy's face. Yet just a short while later, when Tommy makes his first successful sale to Ted, there is not a trace of any bruise on his face (nor is any sign of the bruise seen at any time later in the movie).
When Tommy is rushing to his history final, it's cloudy outside and the pavement is wet as though it had just rained. Yet when he runs into the building and encounters the locked door, the sun is shining and the pavement is completely dry.
At the end, when Tommy is sitting in the boat, we can see as the camera moves that the boat is only in about two feet of water. In the next scene, the boat appears to be in the middle of the lake, and in the next scene he is close to shore again.
Near the beginning of the movie when the group is walking the factory floor, Big Tom asks Danny how his new son-in-law is, indicating that Danny is probably in his early to mid-40s - which he looks. At the end of the movie, Tommy is addressing his employees and asks Danny if he remembers when they used to burn ants together with a magnifying glass as kids, which would indicate they are approximately the same age. Tommy, however, is only 25 years old; 15 to 20 years younger than Danny.
When Tommy and Richard go to Chicago to talk to Zalinsky, they can't get a flight and have to sneak onboard as flight attendants. A few minutes later, when they are outside, Michelle shows up. How did she manage to get a flight when they couldn't?
In the scene where Tommy and Richard stay at the Deer Glen Hotel, Richard makes a comment to Tommy about the moths inside of the hotel room. If you look closely you can see a member of the crew's hand throwing moths in the air at the base of the lamp behind the end table.
At the airport, Tommy's love interest is trying to fly to Cuyahoga Falls, but there's no airport in Cuyahoga Falls. She would fly into the Akron/Canton airport which is about 30 minutes away from Cuyahoga Falls.
When Tommy and Richard come back from the airport, as they pass through town you can clearly see a Toronto Dominion sign (Green with big white TD written on it) on the corner of the street, just as they turn right.
In the beginning of the movie, Tommy rushes to take his American History Final. The first question is "Thomas Jefferson, James Madison and __________ Hancock were Framers of the Constitution." Tommy puts Herbie instead of "John." However, while Madison was at the Constitutional Convention, Hancock and Jefferson were not. In fact, Jefferson was in France as our Ambassador to that nation.
Throughout the movie it is implied that Sandusky relies only on various factories for its economy. However, Sandusky is home to Cedar Point, one of the most popular amusement parks in the world, which brings in lots of tourism to the area.
When Tommy and Richard are trying to board a flight from Sandusky, OH to Chicago, the plane at the gate is an Air Transat L-1011. Air Transat is a Canadian charter operator and would not operate flights between those two cities.
Just as a group of suits are about to enter the work floor of the factory, Tommy's father insists everyone wear a hard hat. Yet on the floor, several employees are not wearing them, violating virtually every safety code imaginable.
When Tommy is changing clothes in the airplane lavatory the end of his tie gets in the toilet, then he hits the flush button and the toilet sucks his tie down with such a force that it pulls his face down to the bowl. In actuality this blue water recirculation type toilet has a metal flapper in the bottom of the bowl and is designed as a simple gravity drain with no suction at all.
Both Beverly and Tommy would not have received Big Tom's shares of stock right away. After Big Tom's death, his estate, including all his shares of stock, assets, liabilities, and so forth, would have had to have gone through probate. The probate process takes many months, if not years, to close, so the Callahan factory would not have been in any danger of a hostile takeover by Mr. Zalinsky. Consequently, because of probate, any outstanding bank loans or monies due Big Tom's Estate would have been handled by the Executor, and the factory would be able to operate as before.
At the beginning of the airplane bathroom scene, Richard's double can be clearly seen entering the bathroom - the double's hair is much more gray than Richard's. Then, visible through the crack in the door, the double can be seen to go left as Richard comes back of the bathroom.
Tommy and Mr. Zalinsky are seen going up an elevator to the board meeting, yet how could there be a crash test level so many floors above the street, containing cinderblocks, concrete floors and test vehicles?
In the scene where Bo Derek exits the swimming pool, she's wearing a bikini. But in the scenes before and after that, characters are wearing jackets and the trees have no leaves, so it would be too cold for swimming.