Years ago, while riding, I was making a legal left turn in front of a driver, who began honking his horn and flashing his lights. Well, I flashed him the finger and yelled a few choic words at him, and continued my ride. The next day, a co-worker started laughing when he saw me. I asked him what was so funny and he said, "You didn't know it was me, but yesterday you were riding your bike, waving your finger around, and cussing like a drunken sailor. And I had my wife and my little son in the car with me." He was the driver of the car, and was honking and flashing his lights just to say hello!
I felt so humiliated by my bad behavior. This was really one of the turning points that made me try to be less angry and reactive, both in traffic and in life in general. That is, I try hard, I don't always succeed, but at least I'm a lot better about apologizing when I do slip up.