road rage

On the way to the station this morning i witnessed some road rage. (Although, is it called road rage if it is a pedestrian doing it?) I didn't see the incident that caused it but came round the corner to see a guy in a suit holding a briefcase, presumably on his way to work, shouting at a car waiting in a queue of traffic. I couldn't understand anything he was shouting so have no idea why he was so annoyed. After a bit of a shout it looked like he was done and he turned away to leave. But no, he wheeled back around, started shouting again with renewed vigour and tried to open the driver's door. It was locked so he resorted to hitting the driver's window with his open hand. And more unintelligible shouting. The driver was sitting looking embarrassed whilst trying to ignore the crazy man outside his window. I didn't see how it resolved itself because by this time i had walked past the scene and had to turn down another road. I wonder what the driver did to so enrage the man?