I'll start: The Stars Wars postlogy was such a disastrous cash grab that it doesn't exist in my head cannon.

This whole thing was a mess.

George W Bush

Highlander 2 was ssssssssssooooooooooooo bad.

Matrix: Resurrections

Totally unnecessary sequel to a not so great 3rd part of a great franchise.

I felt unsafe watching it the whole time.

The Starship Troopers sequels. Which don't exist, but if they did they would be awful enough to pretend they don't.

Boondock Saints ,2

Every home alone past 2, every terminator past 2, the latest Matrix practically apologizes for its own existence. Examples are too numerous, the entire hyperreality we exist in is built on pointless repetition and self-cannibalization.

Our world is running out of resources to turn out profit, so it had started digesting itself and feeding us its over-processed and over-produced communion, like a sleezy street-food vendor dousing their meats in spices, so we don't smell how spoiled their paska is.

That is why everything revolves around the nostalgia: it's not us who are stuck in the past, it's our culture experiencing rigor mortis, and we treat it as the final chance to see its original form, as if the chicken in our tavuk durum hasn't been rotting since yesterweek.

American Psycho 2.

Yeah, there's a direct to video "sequel"

Less of a sequel, but all the remakes of 80s/90s classic movies are awful and do nothing but bastardize the legacy of some incredible pieces of art. The Karate Kid, Total Recall, and Point Break top the list.

Halloween.

Executives butchered what was gonna be an anthology series because they saw Michael Myers as a marketable villain. So now every film in the series has gotta be the same thing again and again with the same monster doing the same things, ad infinitum.

Now I come to think of it that's, like, pretty much the entire mainstream of the horror genre isn't it?

There are only two Shrek films.

Oh, jesus, I just remembered!...

The cute but completely and totally unnecessary A Christmas Story Christmas!

Hot take that might get some shit, but I'll say it anyway:

The Matrix.

The first movie, if it was the only one, was such a sleek tight narrative with such a satisfying ending that left so much open to the imagination that arguably the movie would have more cultural impact today if it stopped there.

Pacific Rim 2

Blues Brothers 2000

Anchorman 2. The first is such a great movie start to finish with so many legendary quotable lines. The second could never have compared to the original. Sticking with Will Ferrell, I really hope noone ever gets the idea to make a Step Brothers 2.

Lost Boys 2 is pretty tragic. Dunno about worst ever.. but first thing that sprung to mind. Those sequels are rough and capture none of the magic of the original. They shouldn't have bothered.

R.I.P.D. 2

Hear me out. I watched the first R.I.P.D. on a flight, expecting it to be enjoyably bad, but it wasn't. Instead, it was just enjoyable. The whimsical lore of combining ancient prophecy with modern people and boring bureaucracy was pretty funny. Was it an absolutely fantastic movie? No, but it was good.

The sequel, however, explored none of the above any further. Instead, it tried to replace all that with a much more dramatic tone. So when I watched this one on the flight back, it wasn't even enjoyably bad. It was just simple and dull.

Most unnecessary, Indiana Jones 4. Last Crusade was a perfect ending. Worst...I submit Grease 2 for your consideration. Not only is it a terrible movie, it is arguably worse than Starlight Express as a musical.

Most of modern StarTrek is pretty much up there, especially Discovery, as that wasn't just bad by itself, it also seriously fucked up the timeline beyond repair and utterly failed at actually doing anything interesting scifi wise. It turned a franchise that used to be thought provoking into mindless pewpew with lots of crying and a complete lack of competency and professionalism. The "fan service" is also excruciating, as it's just name dropping things from MemoryAlpha, while completely failing at doing anything interesting with them.

I give Lower Decks a pass, as that at least understands StarTrek, doesn't mess with the timeline and actually continues where TNG/DS9/Voy left off. But most of the rest should better be snapped out of existence.

It's especially depression as we are right now in a time were serious progress has been made with AI and where a bit of though provoking scifi could actually work quite well, instead we just get reruns of old tropes.

The Sting is a near-perfect movie which wraps up an entire story, spawning an entire genre of copycat clever-twisting ensemble movies. It wasn't the first movie about the grift, but it was the best.

Sting 2 shared similar characters.

Faraway, So Close!

Wings of Desire is one of my all time top 10 movies, as tempting as it was to make a sequel, it never should have happened. It definitely should not have had a pie fight.

Original:
https://en.m.wikipedia.org/wiki/Wings_of_Desire

Sequel:
https://en.m.wikipedia.org/wiki/Faraway,_So_Close!

Conan the destroyer. The first movie (Conan the barbarian) was absolutely amazing, the second one was a cheap cash grab about some super team setting out to save a girl from an evil bad guy.

Terminator 3