"Even as a white guy"... 
Land of the free, is it? Are you saying it's ok for cops to hit people for mouthing off? What's the penalty for being uppity? You know, don't you, that this is real life right, not a Hollywood Die Hard movie?
My point is that you keep hearing that blacks have to watch what they say and how they act to cops. That's true for white people too. Cops are in dangerous positions all the time. They don't really know who's in the car, whether they got a gun in their lap or what, felons who have escaped, or what. So move slowly and follow his commands. Just common sense.
Today, there a huge amount of disrespect towards cops by many. Now I'm not making an apology for bad cops here. I'm just saying that if a person's disrespect rises to a level where the cop feels threatened because of the dangerous position they're in all the time, he could react in an unfortunate way. And he's armed. Just be polite and follow their directions. If you're shooting pictures in a place where he tells you to stop and move on, well, move on. You're going to get into a fist fight with him?