Continuity mistake: On the 20th date, Trish and Andy are sitting on a chair discussing the date and that they are going to have sex. When Andy speaks, her right hand is on his top button. When Trish speaks, its back in her lap. This happens three or four times, all in the same conversation.
Visible crew/equipment: In the final sex scene, a crew member's foot is momentarily seen on the upper right side of the screen.
Continuity mistake: Before and after the dream sequence where he kicks the girl and gives her a bloody nose, the comforter he wakes up with is completely different from the one he went to sleep with, which matched his pillow exactly. When he wakes up, nothing matches the pillow.
Other mistake: When Andy first meets Trish, they are looking at a display of DVD players and VCRs. She points to a DVD player and says "This one looks pretty good." Andy replies, "You don't want that VCR." Although a display card has been deliberately placed in front of it to mask what it really is, the VCR appears to really be a DVD player.
Continuity mistake: During the "Aquarius" montage at the end of the film, Andy's "man-o-lantern" chest-wax job is visible in one cut (with the hair just starting to grow back), then completely gone in the next. Since the bedroom scenes in the song are meant to be from the same night, there's no way that his chest could fill in so evenly so quickly.