During the beginning battle scene. When Kirk Lazarus is speaking to Alpa Chino. In the the first shot when Alpa is walking up to the Kirk a strap on his helmet is dangling down. In the next shot it is up crossing diagonally over the afro pick. In the next shot the strap is dangling down again.
When Lazarus is talking to Tugg about 'Simple Jack' he claims that an actor should never go "full retard" and mentions Peter Sellers (Being There), Dustin Hoffman (Rain Man), Tom Hanks (Forrest Gump), and Sean Penn (I Am Sam) as examples. He claims that Sean Penn is the only one of those to go "full retard" and come away without an Oscar after being nominated. However, Peter Sellers did not win an Oscar either. He received a Golden Globe award, while the Best Actor Oscar went to Dustin Hoffman for Kramer vs. Kramer. (This is rectified in the Director's Cut DVD, where the line about Sellers is removed.)
Both Kevin Sandusky and Alpa Chino are carrying Vietnam War era correct M16A1 rifles, complete with the fixed butt stock, 20" barrel and the three pronged flash suppressor. Tugg Speedman is carrying a modern era M4 carbine rifle. This rifle is distinctly different looking than the A1, in that it has the adjustable length butt stock, 16" barrel with the round fore stock and the modern "birdcage" flash suppressor. This rifle didn't come out until well after the Vietnam War had ended.
Les Grossman says that "Speedman is a dying star, a white dwarf heading for a black hole. That's physics. It's inevitable." But a white dwarf do not head for a black hole, white dwarf is the final state of average and small stars. White dwarfs will eventually become black dwarfs once they cool off, in a very very long time, so long that there's no known black dwarf existed in our universe.
At one point, Tugg says one actor may win a Teen Choice Award, and claims that "they'll slime you and everything!". Teen Choice Award winners get surfboards. The Nickelodeon Kids Choice Awards show is famous for sliming winners.
When Lazarus and Alpa Chino is at the hill looking down at the heroin camp, Kurt is using an ACOG scope to look at the camp, this would be wrong since their characters are supposed be using equipment from the Vietnam era. The ACOG scope was issued to troops during 2003 onwards.
When Portnoy is cut down off the water buffalo, he lands on the ground on his back and the stunt double's arms are still bound and are above his head. In the next shot, Portnoy's hands are still bound, but are over his chest.
After Les Grossman hangs up on Flaming Dragon, he and Pecker sit down to and talk about what will happen if Tugg is killed, and you see the people in the room start to leave the room, then it cuts back to Les and his assistant nods his head to leave and you can see the people leaving the room again.
After Tugg Speedman's performance of 'Simple Jack', he is in a room cleaning off his makeup. When he wipes his face with a wet towel, most of the white is gone. However, when he turns around to meet little Half-Squat, it has reappeared.
During the opening scene, the helicopters are seen from the side and are initially "slicks", and empty. No troops inside, no rocket pods or machine guns mounted at the doors. After diving down and seen from the rear, the Huey's now have rocket pods mounted on the skids and machine guns hanging out of the doors. Further scenes show door gunners and some troops now inside.
After the director and actors land in the jungle the director says he will shoot with his video camera. As he is talking and turning around the position of his hand holding the camera changes. First he holds it from underneath then as he turns and the films camera changes angles he is holding it from the top of his camera.
After Tugg (Ben Stiller) split up from the group, the three can be seen walking through the jungle. Jeff (Jack Black) is walking at the end of the group and shot from 3 different angles while claiming he's tired of carrying the gun. The way of carrying changes between shots from hanging from his shoulder to holding in his hands.
During the assault on the heroin plant, the actors have 4 M16's but there are only 3 people equipped with M16's at the drop-off - Tugg (captured), Sandusky and Alpa. So they would only have access to 2 M16's a shotgun and a M60, not 4 M16's and no other weapons.
When Portnoy is cut down off the water buffalo, and he lands on the ground on his back, the stunt double's arms are still bound and are above his head. Next shot shows Jack Black's hands still bound, but are over his chest.
In the opening sequence, the three Hueys are clearly not carrying any passengers nor do they have door guns mounted,or rocket pods. But, as they approach the LZ, all have door guns mounted with gunners, and first one, then all then helicopters have external rocket pods.
The opening crawl states that American POWs are being held in a North Vietnamese Army prison camp in "southeast Vietnam." In 1969, southeast Vietnam was firmly under control of the South Vietnamese government and the American military. Although this could be chalked up to Four Leaf embellishing his autobiography.
Lazarus presents the Academy Award for Best Actor to Speedman at the end of the movie. This award is traditionally presented by the winner of Best Actress from the previous year. So regardless of how many awards Lazarus has, this Oscar would be presented by a female.
In the opening moments, we are told the location is "South East Vietnam." Later the specific setting is Quang Tri. During the Vietnam War, Quang Tri was South Vietnam's northernmost province. However, it is specified that Quang Tri was the location of the "set" of Tropic Thunder, not that it was the location of the events on which the film was based.
The drug traffickers encountered late in the film, despite being in Laos (Sandusky estimates they're not in Vietnam anymore), speak Mandarin Chinese - a fact noted by Kirk, who uses his crappy knowledge of it to attempt to bluff his way into the heroin plant.
Towards the beginning on the movie when the character gets disemboweled with a bayonet in the stomach, when the attacker removes the rifle (supposedly with the bayonet attached) it is obvious there is no bayonet attached to the rifle. However, since this scene is part of a mega-budget movie being filmed, they probably planned to add in a CGI bayonet.
The north Vietnam flag appear early in the film (the read flag with yellow star). But in South Vietnam, it was not used by the VC. However, the Tayback story is set in an NVA (North Vietnamese Army) prison camp, thus it is accurate for them to have a North Vietnamese flag.
When Jeff Portnoy sees the mountain of heroin he runs over and puts his fingers up by it. If you look at his fingers you can clearly tell that he has already dipped his hands into the fixture during an earlier take.
When they are distracting the rebels with Jeff, Alpa and Sandusky are treading through the water holding up their guns. A close up shows a normal shot of the guns, but from far away Sandusky's gun still has a plug on it.
During the opening credits, the helicopters fly past a chalk cliff face with a distinctive pattern. When the four actors later stumble upon the heroin processing plant, the wide shot of the camp shows the exact same cliff in the background, but it's a flipped shot of the opening credits (or the opening credits were flopped to begin with).
The goof items below may give away important plot points.
Early on, Four Leaf Tayback explains that the plot of the movie-within-the movie is based on his book, but that "Of the 10 men sent, 4 returned. Of those 4, 3 wrote books about what happened. Of those 3, 2 were published." But if Four-Leaf made up the events of his book, who wrote the other published book about the rescue?
When the group is about to leave the landing zone after the director is blown up, Kirk Lazarus is clearly seen removing his shotgun from his side holster. When the angle changes and we see the entire group in line, his shotgun is back in the holster and he removes it again.
At the end of the film, during the Oscar scene, Tugg accepts his Best Actor Oscar. Les Grossman's assistant says "Eight Oscars... $400 Million Dollars... and you saved Tugg Speedman's career." Since the Best Actor Oscar is given prior to the Best Director and Best Picture Oscars, his assistant in theory could not know how many Oscars "Tropic Blunder" would eventually win. And if the film has won 8 Oscars already, they would not leave or stop watching the broadcast before the two most important Oscars are given. However this can be overlooked as it is possible, however unlikely given its 8 wins, that the film was not even nominated for the last two awards meaning that the two men would be safe in leaving early. It's also possible that Les TiVo'd the Oscars, and he and his assistant could have been watching the show later on, after it ended. Thus they would have already known the total number of Oscars Tropic Thunder had won.
At the end of the film, Tugg is presented his Academy Award for Best Actor award by Kirk Lazarus, the previous year's winner. In reality, the Best Actor award has historically (until 2009) always presented by the previous year's Best Actress, and vice versa. However, the back story for the character of Kirk Lazarus includes that he won 'Best Actress' for his role as Gloria Steinem, because as a true method actor he was so convincing in a female role (though in reality he still would have won Best Actor.)
"Tropic Blunder" could have been a documentary, since it was about the making of the film. Therefore, Tugg would have been ineligible for a Best Actor Oscar, since he was just telling his own story in the documentary. However, it is more likely that Tropic Blunder is actually a fictional account of the making of the film, with Tugg appearing as himself, and thereby winning the Oscar.
After the crew first spots the heroin processing plant in the jungle, Sandusky comments that they were in the chopper for hours flying to their drop point, however those Hueys only carry about 2 hours worth of fuel. So they either stopped at various points along the way to refuel (at which point someone might have noticed where they really were or were headed), or they flew for just under two hours and had a refuel point somewhere near the drop point (which also doesn't make sense seeing as how they ended up in/near "the world's hard drug superhighway"). Either way, the copter would have been at bingo fuel and wouldn't have been able to fly them all the way to the drop point, then back to the heroin processing plant, and then used to help them escape.