If a GM's a cunt, their RP's gonna end up smelling and feeling like one big dirty cunt. I'd leave in that scenario. 

Somewhat related, I can't help but roll my eyes at people that act like they take pride in being an uncompromising fuckface(may not be word-for-word) as a GM or whatever else, even if I know they're joking. It's just comes off as agonizingly edgy and it makes me want to pry their kneecaps off with a crowbar.