Other mistake: When Mitch, Frank, and Beanie decide that they are going to have a party they say the party is on a Friday night. When they show the outside of Mitch's house you see the sign for the party and it says the party is on Thursday at 9:00. Then when Frank talks to the guys with the beer bong he says that tomorrow he has a nice Saturday planned. If the sign is right then he would have a pretty nice Friday.
Plot hole: When they are being told they have failed the evaluation, the dean tells them, "Yes, you people did finish with 84%, but another one of your pledges finished with a zero in every category." It then goes on to state that this drops them down to 58%. For one pledge to bring them down 26% there would have to have been less than four pledges, including Blue, i.e. only three actually taking the evaluation.
Continuity mistake: When Dean Pritchard is telling the frat guys that they failed, he flips up the first page on his clipboard. While the paper is flipped up, we can see that there is a line drawn through Blue's name. When he flips the paper back down, Blue's name is no longer crossed out.
Continuity mistake: When Will Ferrell is in the living room for the first time, there are two hockey sticks leaning there. One stick has just a stripe of tape on the blade and the other is mostly taped. He is first holding the one with the mostly taped blade and later it shows him with the other hockey stick.
Other mistake: When Mitch arrives to find the house boarded up, a note is attached to the door. However, the voiceover and the note begin differently. The note begins as 'Dear Mitch, the house is boarded up...', but the voiceover starts with 'Dear Mitch, if you're reading this, you already know the house is boarded up...'.