When debut author Chelsea Banning vented on Twitter about no one showing up at her book signing, she didn’t expect that some of the world’s most famous authors, including Stephen King, Margaret Atwood and Neil Gaiman, would respond with tales of their own nightmare public appearances. “At my first Salem’s Lot signing, I had one customer. A fat kid who said, ‘Hey bud, do you know where there’s some Nazi books?’” King wrote to her. “Terry Pratchett and I did a signing in Manhattan for Good Omens that nobody came to at all. So you are two up on us,”...