My only "no go" is player on player "aggression", in and out of character. Any in fighting, that is allowed/condoned, and I am gone. Anything done to be a jerk towards another player, and its allowed by the rest of the group, I am gone.
Any serious stealing off of one anothers PC's, and I am gone.
So this means any evil, that is allowed to act evilly towards other PC's, and I don't play. If they can keep it focused on the rest of the world, OK.
My caveat for that is "unless agreed to by both parties in advance as something that will forward their storylines and will NOT result in problems in play at the table or away from the table".
For example, the character that joins the party because he's been hired to assassinate another character. Both players know the score in advance, and have agreed to role-play the building tension and one non-lethal fight between the characters.
I find this odd. If I dislike a thing enough to ban it, it stands to reason that the game I'm DMing will be worse if it includes that thing. Who wants a grumpy DM? (At the extreme, the game might not exist if I dislike it enough and for some reason I'm not "permitted" to ban it.)My ire is reserved for people who ban a thing just because they don't like it, without any legitimate, believable explanation as to how banning the thing would lead to a better game.
Oh, one other thing. I hate having a TV on in the same room where we're playing. Talk about distracting!

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.