That was the first thing I thought, too. Then I remembered a time when I observed a police officer overreacting to something, because he had failed to be observant. I tried to volunteer information about what he had missed, and was threatened with arrest for my trouble.
Fortunately, when he became loud and aggressive, his superior heard and came over. I was able to provide the information to her, while he continued to threaten me. She got him out of the area, and defused the situation.
I was very shaken, since I had very nearly gotten arrested for trying to be a good citizen.
There are enough bad cops around to make even honest citizens want to avoid them whenever possible.
Didn't get to the point that I felt threatened. Had a only one or two get obnoxious in the 8 years I've been doing demonstrations. Was able to handle it. Kristinn spoke to the other officers later and their concensus was that he got turned down the night before.