Frankly I think the best thing to do if one of these folks starts ragging on you is just to laugh in their face. Derision is the best legal weapon we have.
They are sometimes so out of control that laughing may get you surrounded...better to walk away from the real "crazies", quickly and silently. They usually shout profanities to your back!
Then they go back to their friendly comfort zone full of other crazies!