Roko's basilisk

http://rationalwiki.org/wiki/Roko%27s_basilisk

“I will say this over again with specifics, so you can see what's going on. Let's suppose that human H is Tom Carmody from New York, and evil entity E is Egbert, an UFAI which will torture puppies unless Tom buys the complete works of Robert Sheckley. Neither Tom nor Egbert ever actually meet. Egbert "knows" of Tom because it has chosen to simulate a possible Tom with the relevant properties, and Tom "knows" of Egbert because he happens to have dreamed up the idea of Egbert's existence and attributes. So Egbert is this super-AI which has decided to use its powers to simulate an arbitrary human being which happened by luck to think of a possible AI with Egbert's properties (including its obsession with Tom), and Tom is a human being who has decided to take his daydream of the existence of the malevolent AI Egbert seriously enough, that he will actually go and buy the complete works of Robert Sheckley, in order to avoid puppies being tortured in Egbert's dimension.”

people have driven themselves to literal insanity with this