There's a lot of things I'd be tempted to say about that I'd never do them, because I just don't see them being done by me right now. I don't like burning bridges though, and like to keep my options open should I one day change my mind.
So aside from the stuff very little people would do. ("would you jump of a building? Would you rape someone?") I don't have anything I can positively say off that I would NEVER, UNDER ANY CIRCUMSTANCE do it.