No Fair Googling the Answer

Question: What may be the worst movie with some of the biggest stars, including Ringo Starr, John Astin, Richard Burton, Walter Matthau, James Colburn, Marlon Brando and Sugar Ray Robinson?

Hint: It's so bad, it's bound to become a classic.

If you don't know, and simply must search for the answer in the modern way, don't give it away. I stipulate that because I am honestly curious as to who has even heard of this flick. I'll post the answer in a day or so, giving everyone a chance to ruminate.