Always be polite to strangers. No matter how tough one thinks he is, there is always someone bigger, badder, or more likely to use violence to accentuate his point.
I don't think I've ever heard that advice summed up more perfectly.
More good advice...
Edit: Ok, you must all go check that out when you have some time to kill and need a good laugh. That has got to be one of the funniest threads I've ever read. Medical "advice" from ER staff that no one should ever really need, but (apparently) too many really do.