I recently DMed a session in which a player sexually mutilated a slain orc (I'll share you the details). I told him that this sort of sadistic roleplaying was out of bounds. The other players generally agreed. The player insisted on defending his actions ("orcs killed my family!") as good roleplaying. I found this excuse to be rather pathetic and told him point blank that if he acted out any thing as vile as that again, he could find somewhere else to game. He didn't take this very well ("you can't tell me how to roleplay!") but he stayed in the group and has never done anything like it again.