I was playing in a D&D campaign a few years ago when, during combat, one of the PCs killed an NPC and proceeded to have sex with the corpse. I was mortified (pun intended) and quit the campaign. The reasons for the act didn’t matter; a line had been crossed and I didn’t want to be part of a campaign or a group of people that would allow that.
Not long ago, I was reading through a horror adventure for my group when a scene called for the death of children. While death is a part of horror, as the father of a small child (soon to be two), I simply couldn’t do it. I rewrote that portion of the adventure.
The above are violent examples, but I’ve also had a player quit one of my games for too much roleplaying. He just wasn’t good at improv conversation, and if I wouldn’t let him dice through social scenes then he wouldn’t play anymore.
So today’s hot button topic is this: What lines bother you enough that you won’t cross them? Does it matter if you are a player or a GM? Have you ever been bothered enough by a particular taboo that you make it clear before the start of a campaign?