My eldest son is 6 years old. He's mentioned a few times that there are boys in the playground who "know what the f-word is" (his words). He knows it's a bad word and not to be said, but doesn't know the actual word itself. I'm concerned that by adding a layer of mystique and playground one-upmanship around the infamous f-word he's more likely to want to use it as and when he inevitably hears it, or hold those who use it in high esteem.
In the spirit of keeping an open dialogue about anything with my kids, I'm keen to talk to him about it, and tell him what the word is (perhaps not what it means), why it's not very nice and that it's no big deal whether someone knows it or not, because ultimately it's not a word that should be used in every day life (avoiding the "it's a grown up word" thing for fear of further adding weight to it).
Obviously this approach carries risks (he tells other kids, joins the "i know the word" club, or even starts using it).
I should add that he has a very strong sense of right and wrong, and I think it's important to trust him with this kind of thing (if I don't show that trust his judgement, how will he ever learn to?), but is it too much too soon?