I managed to get some Jehovah's Witnesses arguing about the interpretation of the bible once. That was fun. I don't think they often talk to people who've read the whole book already.
I persuaded them that it was only fair that if they wanted me to consider their world view, that they considered mine, and got them to agree to take a copy of The God Delusion away to read, and I'd read whatever book they wanted me to read, so we could meet up the following week to chat. I never saw them, or any other Witness, again. The God Delusion was left on my step overnight a few days later.