Before Lars von Trier lost his ability to make films, he made three of the best Danish films ever made: Element of Crime, Epidemic, and Europe, known as The Europe Trilogy. Epidemic is the only comedy among them.
It deals with two writers - the actual writers Trier and Niels Vørsel - who must come up with a script for a film in a few days. They chose to tell a story about a deadly epidemic, which we see clips from during the film, while - unbeknownst to them - a real epidemic breaks out in the real world.
This is a new level of metafilm. It's almost incomprehensible unless you're a film nerd and know a little about screenwriting, but if you do it's funny as hell. I've showed this film to friends, and while I was rolling around on the floor reduced to tears from laughing, they were watching the screen with a completely bewildered expression on their faces. Which just makes me love it even more.
This is an utterly unique film, in every sense of the word. For that reason alone, you should never forget to love it.