Did the same thing with a UPS driver a couple of weeks ago, except the hand slap bit. I ended up talking to his supervisor over it, and like you indicated that I wasn't looking for someone's job, I just wanted them to know that 6" is not an acceptable or legal passing distance, especially when there's an entire lane going the smae direction with nobody in it.

We made jokes about it for two weeks every time we saw a UPS truck while riding...like they were out to get us.