Well, I have racked my brain for... oh, several minutes now to come up with the stupidest ever. What I can provide are the three movies that I managed to think of that really, truly, honestly, were the most UNFORGIVABLY bad movies. Movies that might have been even so lowly as barely tolerable but simply cannot be forgiven for being as bad as they were. So bad that production should have NEVER been completed much less the results foisted on a paying public. UNFORGIVABLE.
Highlander 2
The Avengers
Hollow Man
These were movies with NO WORTHY EXCUSE to have been as bad as they were. They had significant budgets, talented actors, a devoted fanbase... or at least two out of three of these. These were movies which writers, directors, producers, actors and studios should have PUBLICLY AND HUMBLY APOLOGIZED FOR because they were inexcusably pathetic. And what's more they CHARGED people to see them. Endeavored to keep their SHAMEFUL efforts a secret for as long as possible in order to defraud the public out of money. Knowingly foisting upon ua films that in no way could be legitimately described as "entertainment". These movies failed in every way to be entertaining.
There are probably more that I would add to the list but movies THIS bad, this EGGREGIOUS, are rare and fortunately I seldom get tricked into seeing them in a theater. It's one thing for a movie to have no budget and be UNDERSTANDABLY awful. For untalented actors to drag a production into the ground. For producers to have been stupid enough, or desperate enough to back projects that they COULD have known to be unworthy. Plan 9 can be excused because Ed Wood WAS the world's worst director ever. But to have so much potential, so much money wasted by otherwise talented people who SHOULD HAVE KNOWN BETTER, who should have PERFORMED better at their jobs, and then still did their level best to lie to the public in order to get us to pay for the EXPENSES OF THEIR ABJECT FAILURE.
It takes a special movie to earn that quality - UNFORGIVABLE.