I've had to deal with these people as players. As a GM, i make it known that either you're going to bring a PC who's a team player or you're bringing in an NPC in the making. I have no time for bad gaming.

Last time I had to suffer this as a player was when a pick up group occurred when a small group of friends were looking for a GM and extra player, I joined them as a player and a guy I knew was their GM.

The first session I filed it away as "growing pains". They were more murderhobo then what I and GM was used to and my character didn't mesh with that style. GM felt kinda weird but he did the same, filed it as growing pains and being a new group thing.

The second session where I came with a more murderhobo-styled character they continued being a donkey cavity, heaping verbal abuse and overall disdain at my new PC (while leaving the others alone), up to and including letting me die after I went to save another PC. At the end of the session I thanked the GM and the non-donkey cavity people (who were, in all truth really nice and friendly in and out of the game) for the opportunity and told Mr.DonkeyCavity as politely as I could how I appreciated his conduct.

He fed me the obvious pablum: "It's what my character would do!" to which I shut him up with a quick "Then why did you willingly choose to bring a Donkey Cavity of a character?". He stuttered, I left and the GM broke the group up soon after citing creative differences (IE: he didn't really care for unrestrained murderhobos who picked on his friend).