I was browsing around the web and I found some pictures of some of the Washington Square Park Chess players. I haven't played regularly down there since I lived in Queens - about 5 years ago - but some of these pics have a few guys I saw on a recent visit.
Anyway - this information may be a little out of date. Now that I live closer, when I go back to NYC for visits I will try to get some more pictures and post info about more of these shady characters (sarcastic, but in some cases true) so you will know what you are getting into when you go to the park to play.
The guy I have labeled as "psycho killer" is dangerous and I would stay away from him.