Worst studio theatrical movie ever made?

I like that you are looking at those as separate categories. Studio movies aren't always great with production values or the technical side of things, but they usually don't hit the levels of ineptitude you can see with no budget, straight to video or streaming movies.

Superman IV is another sequel that was a mess, with people making it who didn't seem to really understand what made the franchise popular. There were some big budget cuts for that Superman movie because Cannon was in financial trouble, but the real problem was the story and characters. There's a clip from that on YouTube that shows Superman rebuilding part of the Great Wall of China with his supervision. He doesn't fly around and rebuild it, he just scans it. https://youtu.be/rgUgdpP_2K8?t=11.

Whatever it is, I'm sure I haven't seen it.

Jaws The Revenge is a good place to start, it had Caine and a couple other actors of note and it slid off the rails immediately!

What a concept, an enormous killer fish has a grudge against a family in New England and figures out the family is fleeing to the Bahamas and follows them there

Did the shark buy a plane ticket or just watch the jet from the surface of the water and follow the Brodie family to the tropics?

Peeble's 'Islander' accent made the whole mess worth watching though😃

Meet the Spartans? Disaster movie?

Honestly I didn’t think Jaws the Revenge was the worst ever. Sure it was shit and an insult to the original but I think labeling it the worst ever is hyperbole

Caddyshack 2

Die Another Day (2002)

Suicide Squad (2016) is the first one that comes to mind. Even the worst comicbook films are still watchable. They're so bad that they're entertaining

This was just so meh. Absolute mess of a film. It's a film chopped up & stuck back together by the studio. One of the worst experiences I've had watching a film.

Never rewatched it & have no plans to do so anytime soon