According to this story in The Guardian, a new biography of Kurt Vonnegut plays up an unpleasant side of his personality. I wonder whether it does, or whether that is journalistic spin. I wouldn't assume that any biographical subject is going to come out of an in-depth study seeming "nice" all the time. Even I am said to have my grumpy moments.
It sounds like an interesting book, one way or the other. Vonnegut was one of the greats of the second half of the twentieth century. Books such as The Sirens of Titan, Cat's Cradle, and Slaughterhouse-Five are satirical classics. Even though I am probably in the minority, I have a special fondness for Breakfast of Champions.