Revealing mistake: When Will Ferrell is drunk on stage talking about streaking and bends over, the students watching the screen are grossed out. The assumption is he is nude. However, when he starts running off the stage through the crowd you eventually see below his waist, and he is wearing underwear.
Other mistake: All of the license plates show New York, but the palm trees in the background of many scenes remind us that it was of course filmed in California. Either it's set in New York and the palm trees are wrong, or it's set in California and the license plates are wrong.
Suggested correction: The film never says where exactly it takes place and the clues point to a California location rather than a New York one. In the first scene, Mitch is in San Diego for a meeting with his company. He leaves that afternoon and arrives later that night to see his GF involved in the gang bang. He was stuck at the airport for a while due to the metal detector going off on him, and the time it takes to get from San Diego to New York, all the signs point to it being around L.A. or Sacramento where the weather is nice enough to have outdoor parties and swimming pools in November.
Continuity mistake: When Frank is announcing the main event the mic is seen at different distances from his mouth as the camera angle changes.