Fantasy Mission Force.
When we purchased a collection of 5 Jackie Chan films for $5, this is not what we were expecting.
Something involving a group of heros (Under the orders of Abraham Lincoln), ranging from an Elvis impersonator to a medieval knight, as well as a chick on a horse with a Bazooka, and their quest to.. actually I don't know what their quest was. Something about prize money and a big conspiracy and WWII being fought in Canada. And an army of Nazi's in 1970's muscle cars tattooed with Swastikas. Jackie Chan was in there somewhere, I think he had about 5 minutes of screen time.
Takes the cake as the most unexpectedly stupid film I have ever seen, it was hilarious at the time, but I don't think I could ever sit through it again. The whole film was up on youtube a while ago, but I can't find it.