I have to credit blog reader Leighton in making me aware of this adaptation of the Kurt Vonnegut novel, called the worst film ever made by many reviewers. It features Jerry Lewis and Madeline Kahn playing a pair seemingly mentally deficient twins as well as their "beautiful people" parents. It's discovered that the twins aren't actually retarded, but are geniuses with the capacity to solve all the earth's problems. Themes of rejection, prejudice and short sighted lack of compassion for humanity run through the film, disguised by comedic gags and wacky goings-on.
This film fails on many levels, though there are flashes of brilliance in some of the performances. The impressive cast also including Marty Feldman, Jim Backus, Merv Griffin, Pat Morita, Virginia Graham and the voice of Orson Welles (uncredited).
Above are two trailers for the film, uploaded to YouTube by akiragp. It's available on VHS and there was a European release on DVD, but it's a region two, so won't play on some American players.
Obscurity factor: 9 (on DVD in Europe, limited distribution at time of release, not well remembered)