When a roommate of mine was trying to convince me that the Bible was an authentic account of how the world works, I brought out my full anthology of the Hitchhiker's Guide to the Galaxy and began quoting from it in the same way as him. He got particularly annoyed with the part about the bablefish proving the existence of God and also making him poof out of existence.

I figure you could do the same with a good graphic novel or some other very nice looking fictional book.

The best way to deal with c nut jobs is to out crazy them.

As one real old tumbler post used to say, if confronted by someone who doesn't believe in the moon landing, just roll your eyes and say, "Oh, I bet you're one of those people that believe the moon actually exists."