Say it isn’t so!  Patrick Dempsey is facing allegations of poor behavior on the set of “Grey’s Anatomy.” The 55-year-old actor is perhaps best known for appearing in the long-running medical drama for the show’s first 11 seasons as Dr. Derek Shepard, also known as “McDreamy.” In her upcoming book, “How to Save a Life: The Inside Story of Grey’s Anatomy,” author Lynette Rice opened up about Dempsey’s time on set – and the reason for his departure.   She says his diva-like behavior and tension with Ellen Pompeo had become pretty unbearable by season 11, to the point where they weren’t even putting him in every episode anymore. A producer named James D. Parriott says, quote, “There were HR issues. It wasn’t sexual in any way. He sort of was terrorizing the set. Some cast members had all sorts of PTSD with him . . . I think he was just done with the show.” Dempsey himself says, quote, “It’s 10-months, 15-hours a day. You never know your schedule, so your kid asks you, ‘What are you doing on Monday?’ And you go, ‘I don’t know.’ Doing that for 11-years is challenging.” Another crew member says Patrick was miserable, and knew he should have left the show sooner. But he admitted that he stayed because, quote, “They were just dumping money on me.” Do you believe the allegations?