Leifmk
Deity
Here is the problem. Some of these are indeed so bad they are good in a funny way.
Yes, the worst movies are those that are badly-made and DULL in the bargain. Something like Plan 9 doesn't really qualify; yes, it's inept on every possible level, EXCEPT that it actually has something of a plot and keeps moving it along at a decent pace, and while the stuff that happens is stupid beyond reasonable belief it nevertheless manages to provide SOME kind of entertainment.
My personal anti-favourite, which I mention every time a thread like this shows up on a forum I frequent (so I've probably mentioned it here before) was a thing called "Satan's Storybook", which I rented on a whim back in 1989 or 1990. It was an attempt at one of those horror anthology movies that were kind of popular back in the 80s, like "Creepshow", with a framing story and some shorter more-or-less unrelated stories within. It was just horribly made in every way, and dull as dishwater to complete the awfulness. Production values, acting skills, plot and dialogue were all on the kind of level you would expect from 1980s low-budget porn, and indeed I later found out that the closest thing to a professional actor involved was in fact a pretty famous porn star of the time (apparently trying to break into non-porn movies; this was not the right movie to do that with). There was some kind of nonsense about good ninjas dressed in white fighting bad ninjas in order to prevent the birth of the Antichrist or something like that, and even though it had ninjas, the Antichrist (or something) and a serial killer who survived execution (or whatever) it managed to be more boring than getting stuck at the bus terminal all night with nothing to read other than the bus schedules.