Backgrounds and BoobyTraps
In relation to the post on "Growing Up Together" in which I learned a lot about why people felt something nonconsensual was happening in a past game, Ginger Stampley asked:
What happens when another player comes up with a concept that absolutely excludes the request? The player is faced with three unpalatable choices: (1) break your PC's concept; (2) break the other PC's concept; (3) break continuity/the world.
Personally, I believe a player in character creation (only) should never be allowed to "break the world." Character creation is excluded because it is a time and an opportunity wherein one is learning what the "feel" of the world is like. It is a matter of push and pull and getting a character that "fits" into the world made. The GM usually has to do a little adjustment of the world, a little tailoring to the characters, but the essential environment exists in order to facilitate whatever story was built in it.
Once the characters have been created, the world may be "broken" along the lines of appropriate character action. It depends on the GM in regards to how they want to deal with potentially earth-shaking actions.
No PC concept is guaranteed entry into a game. The LintKing has a wonderful character he developed that he'd like to play and, so far, hasn't really fit into any game I've run. It's (obviously) not that I don't think he can play it (although a GM is encouraged to make some level of judgment about that as well) it's that the character hooks make it far more of a challenge to fit any of the games I've run, and still express the whole concept.
A player can be told, "Give me another concept," especially if it's not working. There are players I've told, "Can't do that." Generally I will reject a concept that is too much work on my end, too much relying on my write-ups of information. I have also been known to reject concepts that are too close to others' already accepted, that rely on plot hooks I can't suspend my disbelief for, and for simply being deficient in the "amusing me" rule of thumb.
Now, as for breaking another PC's concept, that's something else, entirely. I will allow it as above: if I've already "got one of those," I might recommend a change. If the player wants to appeal, I'll work out as much as I can. I listen to players. They're the people who keep me in business.
What's more important to me as a GM; a plot consistent with my vision, or happy players? (Heck, if you asked me what the number two reason SwtE failed was, I'd say, "People thought there was a plot.")