Yeah, but Euph, you really can't regard that as "the worst" (or at least I don't) for a few reasons:
--Ed Wood was a hack movie maker.
--Crappy budget.
--No studio backing.
So while yes, most of the MST3K crap does fall into the crap category, I rather suspect it was never meant to be taken seriously--more like a grad school film project, made more for shits and giggles than for art.
Now, if you want to get into "serious" releases, I submit to you the following criteria:
Major studio with promotion, budget, and stars to match. IOW, there's no reason for these movies to suck, but suck they did indeed!
In no particular order, the "WORST" movies ever:
Battlefield Earth
Showgirls
Sgt. Pepper's Lonely Hearts Club Band
Howard the Duck
Gigli
Pearl Harbor
Xanadu
Alexander
Wild Wild West
Street Fighter
Highlander II: The Quickening