16Joss Whedon vs Donald Sutherland
One might think that having an A-list celebrity like Donald Sutherland on board a project would provide a very good opportunity for a project. For the Buffy the Vampire Slayer film, though, writer Joss Whedon (who went on to give us the excellent Buffy TV series) absolutely hated working with the actor who portrayed
Buffy's mentor and Watcher, Merrick.
Sutherland had a habit of re-writing his lines in the movie, leading Whedon to later refer to the man as someone who was rude. Whedon never questioned Sutherland's abilities as an actor, but he still states that he hated working with him, referring to it as a bad experience. Sutherland is also why later writers ended up changing Merrick's story arc in the movie.