Deliberate mistake: When MIB agents exit the lift to get into the main hall of the MIB Office, the lift opens halfway up the wall and they need to go down a little platform. But when K and J return during the lockdown and face the trashcan with guns, the lift opens at floor level, so it can be conveniently peppered with bullets. (01:02:05)
Suggested correction: The building is in lockdown so it is no surprise that the lift is changed to a less flamboyant version. Even in the first scene, there are some doors there.
Deliberate mistake: In the first scene Velma gets sprayed by the hose and slips but gets her foot caught on the chain; hanging upside down, but her skirt doesn't go "up". Deliberate to maintain the "family movie" tone. (00:02:40)
Deliberate mistake: Am I REALLY supposed to believe that a helicopter is capable of hovering above the top of Mt Everest? [In the DVD specials, the filmmakers say that they're absolutely aware that it's not possible for a helicopter to hover above Mt Everest. They just thought it would be a funny scene if a helicopter pulled the dead guy away from the mountain.] (00:02:15)
Deliberate mistake: When Chosen One is dancing in front of Betty, take a look at Betty's face. There is a moment in which the face of the double playing Betty is visible.
Deliberate mistake: At the end when Ali smokes the huge spliff, look in the difference in length between when he first lights it and starts smoking it and when he starts blowing the smoke out. It's about 10 times smaller in the second shot.
Deliberate mistake: When the lady is supposedly in the water with the crocodile, you can see that it isn't her. It is actually Steve in a fat suit and wig.
Deliberate mistake: When Scrat's coconut falls from the tree, it has already had its husk removed. The directors confirm this on the DVD commentary. They may have been worried that a lot of their audience would not recognise a coconut with its husk on. (01:11:45)
Deliberate mistake: When John and his sister Patty are watching the old videos, it shows John saying that he would pay for his niece's college education and the camera is showing them from the side. John says "And that's a promise from your uncle John." and the camera is in front of him showing his face. There is no way they could change camera angles like that in a home movie.
Deliberate mistake: When all the thumbs are at the wall saying "I'm the king of the globe" and "I'm a dentist" you cannot see their legs, so that saved some costume work.
Deliberate mistake: When Mr. Roboto is offering Austin a mushroom, the subtitles lead Austin to think Mr. Roboto is asking him to eat some shit, until Foxy reveals more of the subtitles to say "Please eat some shitake mushrooms." The correct spelling for this kind of mushroom is "shiitake." They had to cheat on the spelling in order to make the joke work.
Deliberate mistake: During the scene where Richard is playing croquet on the lawn in front of the Delta Iota Kappa house, the letters of the fraternity are visible on the front of the house. The Greek letter for "Delta" should be a triangle yet it is the letter "D" in the shot. This is presumably to follow the "DIK" joke that would not be as obvious if written in correct Greek letters.