Continuity mistake: When Michael is talking to Walter, the art dealer, the latter has his hands folded together. In the next shot he has one hand on his lap and the other on the table. (00:35:20)
Continuity mistake: Just after Michael throws his mothers cigarette out of the car, there is a shot from the inside through the front window. There is a large crack in the glass, bottom left of the rear view mirror. When the car is shot from the front, there's no crack. (00:24:30)
Chosen answer: It might not actually have one, in which case, he'd have to go down into the club and use theirs. As for showering, going to his mother's house or a gym membership would take care of that.
Captain Defenestrator