1) teach your girlfriend to drive and put him into her ass so he has to pay.
2) give girlfriend taser
now, i understand there were other people in the car. but, think about this. you're pissed off because of what SHE told you. perhaps there IS more. I'm not saying there is, but c'mon. I've pissed people off on the road more to get back at them for being idiots, but just ONE stop sign and a complete stop doesn't equate that to me. maybe her driving incredibly slow, blocking him in, and THEN making a complete stop... now that's something I'd do intentionally to make him angry...
the opposite side of this: Good on you for wanting to hurt someone who'd even THINK about hitting a woman. I wish I'd had that when someone actually smacked me in the face. I had my husband sit there and tell me 'you deserved it' I looked at him and kicked him in the balls. Then he goes 'What's that for?' I told him, 'You deserved it for not trying to kill him for hitting me, you asshole.'
ok... so yea. I hope you find him... and if you want him whacked... gimme a call.