Twice. Once my fault (technically, though the guy cut me off, and after I rear-ended him he took off like a bat out of hell, so he was clearly up to something shady) and once I t-boned an old man who blew through a red light.
Just today, the guy behind me swerved around me as a light turned green... so that he would be in FRONT of me at the NEXT red light. I was tempted to run into him to teach him a lesson, but, well... fantasies. His car was WAY nicer than mine. More painful for him than for me.