Earlier this week I was taking my wife to the train station and a BMW in the other lane swerved at the car in front of us. I watched for another second and told my wife... "I think that guy is road raging."
Sure enough, at the next light he pulls in behind the SUV (in front of us), gets out and walks over to the driver side window, screams "you were going 40 in a school zone (25mph)" three times, then spit on her (~60 year old woman) window and smeared it all around with his hand.
She was probably doing 30mph since she slowly passed the guy, but this guy thought it was his duty to make sure that she knew she was wrong in the most aggressive way possible. Some people get off on that, I guess.
No idea why that story came to mind just now.