"Why can't I say ‘sucks'?" my son asks. He's twelve, and pretty much everyone he knows uses that word freely. It's kind of a bad word, but not really. It's a crossover word, like crap. Crap used to be a curse word, but now it's moved into the crossover category: not a nice word, but not a curse word either.
It's hard to tell your child that "sucks" is a bad word when the rest of the world disagrees with you. We regularly hear ads on the radio for "Your Marketing Sucks": a book about — well, about how your marketing is not quite what it should be. I guess the author felt he would not sell as many copies if he called his book "Your Marketing Stinks". He may be right. "Sucks" still shocks us, albeit just a little, and gets our attention. It seems audacious to use it in polite conversation.