That reminds me of a idea I have had: Some sort of laser-tag like electronic system that would let you point a remote control like device at someone's car while commuting and thumb up/down them. Then there would be some sort of display that would show that persons karma scrore as a positive or negative number. Get three thumbs up and a thumbs down and you'd have a +2 net score. Someone lets you in in traffic and you blip'em a quick thumbs up. They cut you off or otherwise act like a dickwad, and thumbs down for you. Now I see you with a -xxxxx score and I know you are a top shelf jackass and give you leeway.
, but electronic, and cheap.
Right now I just use weather you are driving an accord or not as my indicator. Something about those full-size Hondas..