Sasha Volokh wonders about the origins of the "nonsense" meaning of the word "baloney". I'd always assumed that the usage is based on its first syllable being identical to that of a certain vulgar synonym (when the former is pronounced, in the American style, with an extended schwa, as in, say, "bull"). The expression "son of a gun", originally signifying a man born aboard a ship, appears to have acquired its current, euphemistically derogatory meaning by the same route.

Anyone with real information, informed speculation, or for that matter an uninformed speculation on this question is invited to comment.