Teri Hatcher and Marcia Cross
These two played seamless best friends on Desperate Housewives, but they truly hated one another in real life. Their biggest fight was actually on set during a Vanity Fair shoot. Hatcher was supposedly trying to steal the spotlight, micro-manage the photographer, and make the shoot about herself. Cross ended up blowing up and threatening to walk off set if Hatcher didn't quit it.
Alec Baldwin and Tina Fey
Not only did Alec Baldwin and Tina Fey star in 30 Rock together, but they were also executive producers. Unfortunately, that meant that there was a power struggle and they butted heads a lot. They bickered, argued, and threw insults at one another like it was nothing. Sources say that Baldwin wanted way more power than he was ever supposed to have.