A Clockwork Orange 

A Clockwork Orange was extremely controversial for its gratuitous violence and seemingly-encouragement of disturbing behavior. Even with the violence and utter chaos of the movie, the improvised line fits seamlessly.  

While the main characters are doing horrific things during a home invasion, apparently, actor Malcolm McDowell decided to start singing, “I’m singing in the rain.” This seems to follow the same pattern of The Shining, where a horribly violent and scary scene becoming even scarier when a moment of calm or comedy is thrown in.  Stanley Kubrick, the same director of The Shining decided to keep this improv in as well.