Your friend may be all right, but I don't like the cops and it's because of things like this. Many of them abuse their power. Having said that, hasn't anyone ever heard of telephoto lenses? Why would I get close and take photos of the cops unless they were way out of line, in which case how do I think they would react? Better to take a few snaps as you're quickly walking away and call 911 and tell them what's going on, and that way it's recorded (hopefully).
Along w/ wanna be cops, my other pet peeve is wanna be press photographers. I have enough experience to stay away from armed police that are already stressed out. Being "a New York photographer" means nothing. To me, that's a stupid person butting in where he doesn't belong and asking for trouble. Like I said, if there's police abuse, there are ways to record that safely and have it reported. You have to use common sense. Or at least be smarter than the cops. Anyone that isn't deserves everything that comes their way.