Or, invite them in, and (politely) try to pitch a conversion to atheism. I usually get sooo close, then you see that programming snap back into place (you'll see their expression change to one of terror), and they suddenly have to leave really fast.
Mormons are more fun for this, but Jehovah's Witnesses are a laugh riot.
Mormons are more fun for this, but Jehovah's Witnesses are a laugh riot.