If Bob is a jerk, Bob's a jerk. The point of my silly example is that the GM just shifts the focus and it's done.Bob then proceeds to make not-nice and threaten the shopkeeper, requiring either focus time, or local reaction, or otherwise telling bob off, or just pointedly ignoring bob, at which point, if bob's the persnickity type, may require invitation to exit. (Not that I'm thinking of doing so. Just exemplar at the current.)
Also, most of my gaming is not in a space I control; I literally cannot boot certain players because, in one case, is host, in another, because of the venue's rules.
Getting the cooperation is part of learning when enough is enough... and part of that is feedback in both directions.
Also, if Bobs are that common in the venue you run in, maybe don't?