Think of negative speech as verbal pollution. And that's what I've been doing: visualizing insults and gossip as a dark cloud, maybe one with some sulfur dioxide. Once you've belched it out, you can't take it back. As grandma said, if you don't have anything nice to say, don't say anything at all. The interesting this is, the less often I vocalize my negative thoughts, the fewer negative thoughts I cook up in the first place.