Continuity mistake: In the bedroom scene the girl is holding a clear cup full of beer. The camera goes off her and when it comes back she is holding a blue cup. The camera goes back off her then on her and the cup is clear again. [This mistake does not appear in the unrated version - the blue cup scenes were shot specifically to secure an R rating from the MPAA because the contents are obscured.].
Continuity mistake: When Finch is moping through the house, depressed, he goes through a door marked "keep out". The door handle is on the left side, meaning that from inside the room the handle must be on the right. However, when he plays with the pool balls, we can see that the door he must just have come through (there's no other door visible) has the handle on the left.
Continuity mistake: In the famous Nadia on the internet segment, there is a quick shot of the computer before Jim starts to get undressed. If you look on the desk next to the keyboard there is a gray t-shirt. It wasn't there when Jim was setting up the camera and Jim hasn't begun to undress yet. Obviously shot after Jim threw the shirt on the Web cam and it slid off.
Continuity mistake: Finch runs into the girl's bathroom when the laxatives affect him. He tries to take out a toilet seat cover, but there are none left. The side shot shows a corner of the box hanging down below the dispenser, whereas when the shot changes to the front, there is no visible corner. It then returns to the side and the visible corner, and back to the front with no corner.
Continuity mistake: When Finch is at the party after the prom and he goes in the room with the sign on the door where Stifler's mom is he opens the door out. But at the end of the movie when Stifler is trying to get in the room there is a chair in front of the door and it opens the opposite way.
Continuity mistake: In the final scene where the boys are discussing their love lives, watch the man eating a cream roll/hot dog in the background. In one shot he takes a large bite. The camera changes angles to one of the boys and quickly returns to the wider shot. The man is deep in conversation only two seconds after biting down on half a hot dog.