John Mayer's Pissed Journalist Asked Andy Cohen If They Hook Up

John Mayer's pissed a journalist asked his pal Andy Cohen if he and John are hooking up -- calling the question demeaning to Andy, himself and the general public. John put all his emotions down in an open letter to The Hollywood Reporter's co-editor-in-chief, who conducted the interview with Andy -- and in it, he says, "To suggest that people are dubious of a friendship like mine and Andy’s is to undermine the…