Audio problem: When Stifler is talking to Finch about how he is going to get with Cadence and does the nipple milking impression, during a good portion of the shot that is shooting over Stifler's shoulder to show Finch's face when Stifler is talking, watch Stifler's lips from the side: you can see they are moving out of sync with what we hear, it was obviously changed and dubbed over.
Continuity mistake: When Stifler is in the linen closet it is completely dark. Finch and friend open the door and the closet is lit. After that they close the door, but the inside of the door remains lit. When the shot changes to the other side, the closet is completely dark again, without a source to light the inside of the door.