Revealing mistake: When Shelly and the girls (the playboy mansion girls) are getting their hair done for her birthday, the stylist is curling Shelly's hair but you see the iron doesn't touch her hair at all. (00:03:50)
Continuity mistake: In the scene after the Zeta sorority girls get their makeovers and are selling calenders in the quad, when all the girls are sitting down Natalie (Emma Stone) is wearing glasses. When it cuts to Shelley (Anna Farris) talking about Natalie being a virgin her glasses come off, but when it cuts back to her, her glasses are on. It goes back and forth a good three times.
Continuity mistake: When Shelley drops her towel and walks around the house nude, in the first shot it appears that the tan lines on her bottom have been covered with makeup. When she stops at the top of the stairs, her tan lines are then plainly visible. Later, when she has dinner with Oliver, she talks about her butt and specifically says that she doesn't have any tan lines.