During the scene where Jim has the music up too loud, Bill comes in and it appears that he yanks the plug out. After he leaves, Jim turns it back on by hitting play, not by putting the plug back in.
The mark on Thomas Drake's face after he and his friends hit their heads together in the restaurant.
Several seconds before Reggie gives Bill a maple bar, the tray containing the maple bars is about six inches to the right of the divider in the middle of the shelves. From that moment, Reggie is at the cash register and Anita is talking to Bill, so there is nobody else near the tray. But when Reggie comes back into the scene to grab the maple bar, it is flush with the divider even though there was nobody else behind the counter who could have moved it.
When the guys are driving to the strip club, you can clearly see a cop car blocking a side street to prevent any cars from interrupting the filming on the main street they are driving on.
Jim corrects Tony, telling him not use the phrase 'Nam instead of Vietnam, and that veterans hate when regular people do that. He then almost immediately uses 'Nam when telling his story about Charlie getting spit on by a bank teller.
Billy tells Jim that he's five years older than him as Jim is 16 years-old. But in a previous scene, Billy says he's almost 19.