I DM for a group of a group of rather intellectual players. They like to discuss the situations at hand and really try to do the right things. I use that a lot by posing them with moral questions and missions where the "good" solution is not always obvious or even contradicts the mission target.
So far this worked out very well, but last round a new player joined our game. She plays an impatient, man-hating Amazon (her self-chosen description). The man-hating part kinda does work since she frequently gets into arguments with the male players, which is funny, but the impatient part is the real trouble.
Whenever the group stops to discuss something, she interrupts and just wants to fight stuff. Whenever they talk (in character) about anything else than the mission she interrupts saying that it doesn't matter or doesn't help the group.
Also, whenever someone says anything against her, she does get a bit offended.
In the end of the mission I put a moral choice, where they had to retrieve a magical object, but by doing so kill a whole forest and everything within it. While the rest of the group was discussing it, and trying to find a different solution (of which there where some), she just went ahead and cut that object from it's socket, thus killing the whole forest. This in turn will have negative consequences for the group and the world they live in in the sessions to come.
I expected her to be like that so I included a couple of things where only thinking would get them ahead and just charging into fights would hurt them, but she doesn't care about consequences and just barges in.
Since she doesn't fit into the group at all, I'd usually just put her into another of my groups where she'd fit better, but she's the girlfriend of one of the core players of that group, so I can't do that.
I thought about having an NPC, that the rest of the group know, join the group and keep her in check every time she goes overboard again, but I fear that by limiting her I'd take the fun away for her.
My problem here is not that I don't want the players to commit mass murder. I have another group that is quite murderous and that's fine. The problem here is that I have a quite homogenous group and one player that really doesn't fit the group. It's not even so much about her murdering people (which can be quite fun in an otherwise good minded group) but that she is disrupting the kind of play that the other players want to have.
Do you have any ideas what I can do here?
This is not so much a My-Guy-Syndrome, but rather a clash of expectations. I talked to the player in question. It is really not about her "having" to stick to her character, but rather that her character reflects herself. She says of herself that she is impatient and that she rather wants to fight than to discuss. In the end she wanted to get transferred into my other group, which is more combat-oriented and generally more diverse.