I have a few things I like to do...
1. If its at night I get right up on their ass and ghost them with all my lights turned on bright.
2. If its day I still ghost them (if they slam on the breaks its not like they will be around to tell anyone what happend)
3. Crack a smile
4. I have done double birdys WITH a smile going ear to ear
But basically dont get mad at it, they are just poor people that can't afford to drive something as awesome as a hummer and if they are some eco tree hugging fruit cake they shouldnt be driving at all..let alone breathing since they are just wasting oxygen for me.