CBS threatened to sue an author over his book’s shocking claims about hit reality TV show Big Brother, but he’s refusing to back down. Brody Stuart-Vernerexclusively told RadarOnline.com that he stands by “everything” in his book, The Big Brother Bible: 25 Years of America’s Summertime Guilty Pleasure, including claims that the show “intentionally cast racists” and “categorically avoids casting transgender applicants” on the show. Stuart-Verner exclusively told us: “CBS’s lack of response, particularly when asked to specify which areas it disagrees with, speaks for itself.” The author noted he…