Old Friends - S1-E3
Other mistake: This Jan Haseck assassin, who has either multiple allergies or else one allergy to a very common substance (peanuts), could never do any espionage work, as it would make him too vulnerable.
Hard Bargain - S1-E9
Other mistake: When one of the kidnappers knocks on Michael's door, it shows him undoing a sliding barrel bolt before opening it, but the bolt does not have anything it slides into on the door frame rendering it pointless, especially as the door opens inwards. (00:30:20)
A Dark Road - S3-E10
Other mistake: In this episode, Michael, Fiona and Sam are boxing in the bad guy's Corvette, trying to make him crash. Despite repeated hits to the side and back of the Corvette, just before the Corvette crashes, there is no visible damage on the bad guy's car.
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