Here in the Deep South, of course, bible-thumpers are prominent. You can rarely get away from them.
I, personally, have no problem with them. Freedom of speech is freedom of speech, period. However, most people don't seem to understand that, and arguments will often ensue.
Whenever this situation arises, I consider it my duty to deflate the tension as much as I can. The following tactics are useful.
- Join the crowd and start shouting your own custom-made slogans. Eg. "I like pie!" or "Gay porn!" or "Revolution now, evolution never!"
- Join the crowd and start shouting canned slogans. Eg. "Attica!" or "Show us your tits" or "USA!" The latter slogan is choice because you may be able to whip the crowd into an ultra-patriotic frenzy with it.
- Join the preacher and start taking his side. Begin your defense with fairly lucid statements, then gradually veer off into more surreal territory. If you do it well enough, you'll have the preacher agreeing to such statements as "Jesus is like a cowboy hat."
- Stand across the street from the preacher and start preaching yourself. Pick anything. Talk off the top of your head, or use some other source. My favorite has always been the TV Guide. "Today's reading comes from the Book of Happy Days, season one, episode 118." After a while, if you aren't attracting a crowd yourself, gradually make your way over to the other side of the street. Don't make it too obvious, but eventually you should be standing shoulder-to-shoulder with the other minister, all the while preaching your own gospel in a very loud voice. The resultant din can be very gratifying.
Of course, when you look like I did in college, just joing the preacher's side is enough. There's an element of the bizarre in seeing a pierced, mohawked, bearded fat man arguing in favor of hard-line religion. It tends to take the wind out of one's sails.
Okay, so the important thing to remember is never take up a specifically antagonistic standpoint. It's your job to make everyone look silly, not get embroiled in some ridiculous argument.
That's it. Use your imagination, and have fun.