What's the worst thing a GM can say to you?
"You're playing your character wrong."
Which a GM actually said to me once because I was running a pacifist cleric and wouldn't kill undead that were trapped in 20 foot pits with no way out, even though my chosen god had no problems with the undead and I'd told him I was going full pacifist at the start of the game. I pretty much quit at the end of that session.
"You suffer X because you didn't specify that you were doing Y."
Where X is a trap, poison, attack, or whatever, and Y is something anyone with two brain cells to rub together would be doing in the situation. Examples include "You get hit by a fireball because, after the last two booby-trapped chests, you still opened this one from the front because you only said 'carefully' and not 'from behind'," and "You are surrounded by an angry mob in the middle of the night because you didn't say you stopped looking into windows after the first ten people started following you around and before I rolled the second die."
Yup. Not a fan.