Adam Gorightly's Historia Discordia tells the story of the prank religion Discordianism. I wrote about the book, and about Discordianism more generally, in an article for io9. Here's an excerpt:

History does not record Robert Welch's reaction when he received a letter on Bavarian Illuminati stationery in 1970. Welch was the founder of the John Birch Society, a conservative group with a paranoid bent, mostly focused on communist conspiracies but also willing to expand its gallery of villains to include other secret cabals. The Illuminati are an 18th-century secret society whose alleged efforts to control the world were regularly decried by groups like, well, the John Birch Society.

Welch may have been a nut but he wasn't a fool, and he was probably pretty sure someone was pulling his leg by the time he saw that the note had been written by "Ho Chi Zen, Cong King of Gorilla Warfare." But I like to imagine that curiosity compelled him to read on.

"We have been meaning to write you for some time," the message began. They claimed they had held off until Harper's magazine—which, the letter assured him, the Illuminati controlled—had interviewed Welch in its August issue. It continued: "All this is in keeping with our new policy of allowing alert and sophisticated persons such as yourself and your followers and associates a more comprehensive review of our activities. For with 96.5% of the entire world now under our collective thumb, we just no longer see any point in sneaking around behind the scenes all the time."