+3
Vivian Vance and William Fawley who played the Mertzs on the long-running I Love Lucy dispised each other. But Vance and Ball became good friends and Fawley and Arnez were buddies, although Arnez told Fawley--a boozer--early on that if he ever showed up on the set drunk he would be fired.
Although successful on the screen together, Mae West and W.C. Fields couldn't stand each other. In a scene in My Little Chickadee, they're supposedly sitting in a railway car facing each other--the camera cuts to Fields for his lines and then to West for her lines: actually they weren't even on the same set together, each having filmed their parts separately and then were edited to appear they were talking.
Marlon Brando did the same thing with Dennis Hopper in Appocalypse Now--wouldn't let Hopper on the set in a scene where the two characters were supposed to be talking to each other. They had to shoot the two separately and then edit it together.
W.C. Fields took his work very seriously and was extremely touchy about anyone interfering with him while he was working. He and comedian Ed Wynn both were employed at one time in the Ziegfield Follies. One night while Fields was doing his famous bit about playing billards, Wynn came out on stage behind him and started mugging. Fields noticed that the audience was laughing at the wrong times, looks behind him, sees Wynn, and breaks a pool cue over Wynn's head knocking him unconcious on the stage. Fields then proceeded with his act, and no one dared go out and get Wynn until after Fields finished his act. As I recall, Wynn was badly injured and had to be taken to the hospital.
Someone already mentioned that Bette Davis didn't think Errol Flynn was a real actor. There's a scene in one film about Queen Elizabeth and Essex, with the two playing the respective leading roles in which Davis slaps Flynn and, whether on purpose or accidentally, she really wollops him. If you ever see that scene, watch Flynn's reaction--that's real hate in his eyes and he tenses up like he'd really like to pop her back. I understand that years later after Flynn's death, Davis was watching that film and commented, "You know, he really wasn't a bad actor after all."