That is some insane behavior. I had a cop pull some aggressive **** in traffic because of me one day...
I think it's so ironic that when I'm riding around town, I'm most worried about both 'professional' drivers
(delivery, taxi, etc) and police officers...

Of course, tapping a car is just as much a provocation as flipping a bird or mouthing obscenities.
Wrong place, wrong car, wrong time for that messenger.