For actors, co-starring in a movie or TV series together can mean months or even years of working very, very closely.
So if you don't... like each, well that's got to be hard. Especially if your characters are besties, or in relationships.
In some cases, perhaps the best acting of someone's career is acting like they don't find their castmate insufferable.
Here are a number of co-stars you may not know don't exactly get on in real life like their characters did on screen.
Sarah Jessica Parker and Kim Cattrall.
Perhaps one of the best-known co-star feuds is between Sex and the City's Sarah Jessica Parker and Kim Cattrall, who played best friends Carrie and Samantha in the TV show and movies.
Things first ignited in October 2017 when Cattrall appeared on Piers Morgan's chat show and said she wouldn't agree to a third Sex and the City movie because of a "toxic relationship" with Parker and her co-stars.
When Cattrall’s 55-year-old brother was found dead in early February 2018 and Parker publicly expressed her condolences, Cattrall couldn't stomach her sympathy, firing back: "you are not my family, you are not my friend. Stop exploiting our tragedy in order to restore your 'nice girl' persona".
Parker said she was "heartbroken" by Cattrall's recollection of events.