Naya Rivera and Lea Michele
Everyone knows that Naya Rivera and Lea Michele did not get along. At one point, Michele requested that Rivera get written off the show. Eventually, the request was granted, and Rivera was written off two episodes before the season finale. The rivalry was real.
Chelsea Handler and Heather McDonald
Comedian Chelsea Handler had a show called Chelsea Lately. Heather McDonald often co-hosted with her. Everyone thought that they were great friends, but that was never the case. Apparently, McDonald never felt any job security and "lived in fear" of losing her career. Handler, not enthused by that, said that she was always free to leave the job and find something else.