I got accosted by one of those "Convert now or burn in hell for eternity" nutjobs myself.
I simply said, "You know, I'd normally LOVE to let you do your little magical wishing ceremony with me and all, but I don't really think Satan would appreciate me talking to you."
Yeah, I actually said that to a custy, and even got away with it. Our super awesome security was there and I was outside so the audio wasn't recorded.
Security simply said, "No, no, didn't hear anything like that."
--Terah The Gas Slave