The New York Times tells the story:

Timothy Trespas, an out-of-work recording engineer in his early 40s, was sure he was being stalked, and not by just one person, but dozens of them. […] He would see the operatives, he said, disguised as ordinary people, lurking around his Midtown Manhattan neighborhood. Sometimes they bumped into him and whispered nonsense into his ear, he said. […] “Now you see how it works,” they would say. […] At first, Mr. Trespas wondered if it was all in his head. Then he encountered a large community of like-minded people on the internet who call themselves “targeted individuals,” or T.I.s, who described going through precisely the same thing. […] The group was organized around the conviction that its members are victims of a sprawling conspiracy to harass thousands of everyday Americans with mind-control weapons and armies of so-called gang stalkers. The goal, as one gang-stalking website put it, is “to destroy every aspect of a targeted individual’s life.” …

(It gets ‘better’ …)