I find it hard to believe that people who believe the Earth is flat really exist in substantial numbers today, and yet here is someone who deals with them on a near-daily basis as they meet up at their mobile planetarium. Their thread on how they deal with them is great and likely applicable to other kinds of conspiracy theories and Science denial. I was not at all surprised that their book recommendation at the end was The Demon-Haunted World (affiliate link), which is a great book.