Factual error: One character says he is pledging a fraternity, but there are no fraternities at Harvard. They have Fox Clubs, as is correctly stated later in the film.
Other mistake: When the guys find out that they've passed the THC test, Jamal turns to Silas and asks if they're still high on the ivory. At the moment he asks, an elf walks across the room. This is supposed to be a figment of their imagination as they are high, so why does the woman at the desk watch the elf too?
Continuity mistake: When I Need Money is "stealing" Gerald's bike when he rolls it down the hill it has a black pocket thing of some sort attached to the frame but just before it hits the truck it disappears.
Continuity mistake: When Methodman and Jamal first meet in the car, the head on Methodman's toothbrush (in his hat) moves from towards his face to away from his face.