John "McNasty" McCain
In his 1992 Senate bid, McCain was joined on the campaign trail by his wife, Cindy, as well as campaign aide Doug Cole and consultant Wes Gullett. At one point, Cindy playfully twirled McCain's hair and said, "You're getting a little thin up there." McCain's face reddened, and he responded, "At least I don't plaster on the makeup like a trollop, you cunt."
The use of profanity in the abstract isn't a problem, but McCain's dropping the c-bomb on his wife (especially over something as trivial as thinning hair) raises the issue of his temperament. If he can't--at a bare minimum--be civil in discussion with his wife, what kind of treatment can the rest of us expect?
McCain later claimed that, "if I lose my capacity for anger, then I shouldn't be president of the United States," but I'm more concerned about too much rage in the Oval Office than too little. (There's also the minor matter of attacking the right target, with which the current administration has had several problems. Would a McCain administration do any better?)