I will always try first to get away from preachy people. Even if I wanted to I couldn't lower myself to get confrontational with someone like that. What works best for me if they follow me or wont quit is extreme sarcasm, supplemented by doses of patronization. Seems to work so far anyway :-)
"When did I realize I was God? Well, I was praying and I suddenly realized I was talking to myself." Peter O'Toole.