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.]. (00:13:20)
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. (01:16:30)
Character mistake: When Jim gets home and finds the apple pie on the counter with a note from his mother, the note reads "you're favorite", rather than "your". (00:31:40)
Audio problem: In the prom scene just before Heather is looking around and looking bored, the drummer is tapping on the hi hat, but the sound is a crash cymbal.
Other mistake: In the opening scene where Jim is watching the encoded TV and his mom comes in to say goodnight, after she kisses him if you look in the cracks of the shades it is light outside. It's day, not night. (00:01:07)
Visible crew/equipment: When Jim walks to Nadia the first time - right after he trips on the couch - a light stand is seen right at the left edge of the screen. This was pointed out in the DVD. (00:08:57)
Revealing mistake: During the prom scene, especially during the song "(Don't You) Forget About Me", none of the band guys (especially the older man keyboard player) are actually playing their instruments.
Visible crew/equipment: In the Internet scene, Jim tosses his shirt over the webcam on top of the computer so nobody will see them. It shows one shot in Jim's bedroom of the shirt starting to slip off the computer, and the next shot is in Kevin's room seeing the shirt fall completely off. While they show the shot of the shirt falling through the computer, you can quite visibly see the hand that pulls the shirt off on the left side of the screen. (00:46:45)
Other mistake: When Jim is fooling around with Nadia, it shows a cameo appearance by Blink 182. It's obvious that the three people in this cameo are Mark Hoppus, Tom DeLonge, and Travis Barker. Travis Barker was the replacement drummer for Blink 182, when old drummer, Scott Raynor, left. Yet in the credits, it credits Scott Raynor, the ex-drummer, as being in the cameo. (00:47:31)
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. (00:48:32)
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. (00:58:35)
Continuity mistake: When Nadia is going through Jim's drawer in his bedroom, a tub of Vaseline magically disappears from one shot to the next. In the same scene on top of the drawer a small white box appears at the same time the Vaseline disappears. (00:45:18)
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. (01:16:50)