One of the most famous examples is probably Patrick Swayze and Jennifer Grey.
They first worked together on Red Dawn, and didn’t get along, reportedly having very different personalities — Grey somewhat sensitive and emotional, Swayze more “macho” and prone to making fun.
So when Swayze was cast as her love interest in Dirty Dancing, Grey was said to be none too happy at all. The friction between the two continued throughout filming, with professional dancer Swayze easily losing patience with novice Grey, and Grey becoming emotional when given criticism.
That famous scene where they’re practicing the mambo, and he slides his hand down over her underarm? Where she keeps laughing, and he gets frustrated? That was real, and not in the script. Grey was extremely ticklish, and Swayze’s clear frustration at her inability to keep from laughing was 100% genuine.
Still, despite the fact that they reportedly didn’t even speak to one another outside of their takes together, their chemistry in the finished film was undeniable, and today, it’s a classic.