There was someone a couple of years who posted here about how he really got messed up in one of those less desirable neighborhoods on his commute. I think his rule (that he broke that time) was to do whatever was necessary to stay far away from large gatherings of people. Any more than 3-4 you should be on the other side of the street or turn a block early to avoid them. People in general aren't bad, but once they're in a pack, that all changes.