A new biography of now-retired talk show host, David Letterman, portrays him as a miserable man who is more self-loathing than self-critical. The book was written by author Jason Zinoman, and it’s titled, “Letterman: The Last Giant of Late Night.” One longtime show writer told the author, “He was never truly comfortable unless he was seething with unhappiness at something.” Letterman’s staffers say he became harder to work with as his comedy took an evil turn. The book says that one night after his “Late Show” ratings lost to both “The Tonight Show” and “Nightline,” Letterman became enraged. A comedy bit called for a life-size Letterman doll to sit in the guest’s chair. Letterman punched the doll, and the audience laughed as he continued to beat the doll. The 580-seat theater eventually went silent as Letterman fell into a frenzy of punching and slapping his plastic alter ego. Letterman’s anger wasn’t all directed inward, and he became upset with pretty much everyone on the show. Things got to the point where the show’s executive producer barely spoke to Letterman and their relationship was strained. One writer says that at the end of the show’s run, Letterman would tell them every night what failures they were.