Continuity: When Dean and Crystal are talking in the lunch line, the same female extra walks by twice in only a few seconds.
Revealing mistakes: When Charlie Bratley is smoking a cigarette outside with Crystal, the cigarette he is "smoking" is not lit.
Factual errors: The "tuba" that Charlie Bratley plays is not a tuba at all but a euphonium. A band student would know that.
Continuity: When Dean is trashing his room, he whips the chair away from the desk. When the camera cuts back to the desk, the chair is still there.
Revealing mistakes: Before Dean unlocks the door to Troy's apartment, there's a shot where you see Dean from inside Troy's apartment. In that shot, you can see the gap between the door and the door frame that the deadbolt is not locked. You can also see the thumbscrew on the door knob is in the typical unlocked position. But Troy gets a hidden key to unlock a door that's not locked.
Factual errors: The scene where Billy looks up at the sky and identifies an F-117 as a Tigershark. The F-117's name designation is "Nighthawk." The "Tigershark" refers to the F-20 designed and built by Northrop Corporation during the 1980s but was not adapted by any of the US military forces.