Other mistake: In the scene where Emily is throwing away all of Steve's stuff, she discards a disco ball, commenting, "Who decorates like this anyway?". But, later in the film, when Steve and Emily are in bed choosing college courses, there is a disco ball (like the one Emily discarded earlier) at the top of the bed. Wouldn't she have thrown that one away too?
Other mistake: In the scene where Steve and Doug are trying to find an ATM to pay off the bouncer at the Roxbury, they keep stopping and starting abruptly. The hanging plants in the back of the truck swing, but the plants sitting on the shelves (particularly the one behind Steve's head) don't move at all and appear to be glued onto the shelves. This is especially visible when the van gets rear-ended by the yellow sports car, the plants don't even budge.