Deliberate mistake: At one point they use a Red Ryder BB gun (Yes, just like in A Christmas Story) and the guy says "You pumped it more than twice, didn't you" to his female counterpart when they shoot the bird. Red Ryder BB guns cannot be cocked/pumped more than once, due to the simple nature of the toy gun that it is.
Deliberate mistake: When Carrie is hiding in the locker room to record John talking with his friends, it's clear that her camera is behind the vent, and the openings in the vent are closer together then the diameter of her camera lens, however we don't see the vent slats in the camera view or the replaying of the video footage in a later scene. Not to mention the fact that she isn't holding the camera steady. This is impossible.
Deliberate mistake: After Ashley gets covered in mud, for the next five minutes or so of the movie the amount of mud on her constantly changes between shots, especially on the back of her head.
Deliberate mistake: There is a huge security breach in the scene with Robin Williams and Christopher Walkin walking at night. The Security SUV limousine is more than 30 metres away from them. It should be pacing them in case of an emergency and be right next to them on the sidewalk. It appears the reason it is so far back is because at the camera angle the scene is shot at, it makes for a good background element which you would not see if the Secret Service followed protocol.
Deliberate mistake: After Doug finds where Minuti was killed and set on fire, he walks over to a dock where he sees Minuti's arm being eaten by alligators. Minuti had been dumped in the water 4 days prior, yet his hand is perfectly intact with no signs of burning, bite marks or weather/water damage of any kind.
Deliberate mistake: The first time the warriors ride out during the full moon, the shot of the moon shows that it is in the phase of "half moon".
Deliberate mistake: When Jenny writes "dick" on Matt's forehead, she does not stop the beam but the word is written with the letters separated.
Deliberate mistake: When the police blitzes the "traditional English breakfast" joint, in the background the menu display advertises "Omlettes", and in the close-up on the owner you can read the word "Mashrooms." It's surely deliberate to show how the joint is not exactly ran by purebreed English people - although it should be noticed that there is an inconsistency with previous scenes when the board was different, and even the word "Mushrooms", handwritten, was spelt correctly. (01:23:00)