We've deliberately tried to steer clear of rewards/punishments/bribes/threats as I want the kids to develop the ability to decide for themselves - without external motivation - what is the right thing to do. I have tried these things at times, nonetheless, and found them of limited utility! They don't really work with my DS, anyway.

Getting down and talking to DS helps. Finding out what is motivating his acting out. Also, doing or saying something really silly to break the mood helps. Suddenly he's off on another tangent and no longer being abusive.
Sometimes when I'm really tired or strung out I yell and carry on like a three year old and that doesn't work at all! No one's perfect, hey?