Humor Risk is considered to be the film debut of legendary American comedy juggernauts the Marx Brothers. A short film released in 1921, little is known about it save for the fact it reportedly sucked so bad and so hard that Groucho Marx is rumored to have destroyed the only known copy in existence.
The story goes that the film was screened only once, supposedly to a rowdy crowd of teenage boys described by Groucho, in an interview where he may or may not have been serious, as "backwards." These boys reportedly kicked up such a fuss and made fun of the film so much that the elder Marx brother destroyed the film in a fit of petulant anger. The veracity of this tale is sadly difficult to ascertain, and it's alternatively rumored that the film was simply lost, with one version of events suggesting the only print was left on a bus.
All we know for sure is that the film never saw the light of day again and that a copy has never been found, meaning that if it wasn't destroyed on purpose, it was almost certainly done so by accident.