What makes a movie bad is that it lacks some perfection that a movie ought to have: good acting, good directing, good cinematography, lighting, sound, writing, plot, etc. The more of these elements you remove, the worse a movie gets. Well, all of the movies that get voted "worst" on these sites still have a lot going for them. They have enough going for them, for example, that they were capable of being widely distributed and viewed by enough people for them to be known as being bad. For example, "The Room", which was the personal project of some weird guy. It's terrible. It has bad acting, no plot, terrible writing, and is cut together poorly. (Or so they tell me.) But it is still better in pretty much every respect than the average film made by a high school student and shown to an english class. And it's better than probably hundreds of professional movies that made it through production and were never distributed widely enough to be well known. Consider the sing-a-long life action drama "Kids Praise 4" featuring Charity Churchmouse and Psalty the Singing Songbook. (This video was a feature of my childhood. Fascinating in retrospect.)
I don't care how much fun you had throwing spoons at Tommy Wiseau, or whatever people do when they see The Room. This is definitely worse.
Moving on, my point is a basic one: genuine negative superlatives aren't really a thing, because the limit of imperfection is when something has no perfections at all, and this is non-existence. And before you get to the point of something not existing at all, things get very, very boring.
What's the absolute worst movie ever? One that was never made.