The next time someone asks you not to spread gossip that they themselves have just said to you, simply say, "If you really didn't want anyone to know, you wouldn't have shared it with me. Not only am I going to tell everybody, I'm going to tell them you told me."
Of course, this assumes you hate the gossip of others as much as if they were actually gossiping about you (which they likely are, but usually only if you are either engaged or disengaged in gossiping, too). That's a safe assumption, right?