When a studio commits to a movie, they take a gamble that their lead actors are going to behave in a professional manner and get along with one another. Even if said actors don't quite see eye to eye, the film-makers have to hope they'll put their differences aside for the good of the picture.
It shouldn't really be that much of a gamble, to be honest, because human decency should prevail, but Hollywood seems to breed monsters like nowhere else. It is, after all, a place where egos run higher than anywhere else on the planet.
Movie sets are notoriously stressful places, and the pressure involved in shooting a film can bring out the worst in anyone, resulting in on-set feuds, creative arguments, and halts in production. Generally, though, these are things that nobody wants to happen and the actors will try to avoid them.
And yet there is something of a Hollywood Black List of actors who seem to have consciously defied the common goal to make a good movie by going out of their way to abuse, annoy or put off their co-stars.
Whether it's down to jealously, resentment, ignorance of duty, outright contempt, an inferiority complex, a desire to "go method," or just no discernible reason at all, it happens more than you'd think...