The title says it all, folks. Give me your worst of the worst.
I saw Star Crash.
That really should cover #1-5 all by itself, but I’ll try to actually think up some others, later.
Do the Star Wars prequels count as “science fiction” movies? If so, then those three would be on my list.
Star Wars: The Phantom Menace
Stargate
Battlefield Earth
It’s late and I can’t think of two more. 
Battlefield Earth
Starship Troopers
Armageddon
Mission To Mars
Keanu Baarata Nikto, aka The Day the Earth Stood Still
Do I need to explain? 
I can’t think of any. It’s a win-win genre where good is good and bad is still good.
In no particular order:
Battlefield Earth: Good lord, why? The director when to the Batman (Adam West version) school of directing. Notice in the scenes in the Psyclos, or whatever the aliens were called, the camera tilts a few degrees. Just like in episodes of Adam West’s Batman series when filming the bad guys at their lair. Also, 1,000 years after the invasion of Earth and Harriers that have been laying around all this time are repaired and used? WTF? I actually find this movie somewhat entertaining because it’s so bad.
Starship Troopers: A controversial movie. Yeah, I saw it, and no, I don’t care if it was supposed to be a satire. It just wasn’t a very good story on it’s own and that’ s before taking into account the silly tactics and mind numbingly stupid asteroid attack on Earth.
The Day After Tomorrow: This movie bored me to tears in ways that Starship Troopers and Battlefield Earth didn’t. It was ham fisted and overly preachy to boot.
Independence Day: I can think of very little to say about this movie that is nice. The closest I came to having an actual emotional reaction to this movie was when the dog almost died in the tunnel. Weird, I almost cared about the dog but the death of millions had no effect on me.
Wing Commander: For many years this has been my gold standard for bad movies. ie. If I saw something like Independence Day I’d say “At least it wasn’t Wing Commander.” Where to start? There’s a scene were a damaged fighter is pushed off the flight deck into space. Upon being pushed off the deck it immediately falls in the same manner as pushing a modern plane off the flight deck of an aircraft carrier. What takes the cake is the scene where a space ship is using what appears to be a sonar device. Fans of the movie will handwave this away but it was really goddamn stupid. Add to that the story wasn’t interesting and you’ve got a really really bad movie.
Honorable mentions go to Lost in Space…which could have easily made this list.
battlefield earth, lol dutch angle
dracula 3000, we ran outta money so thats the end of the movie
starship troopers 2, incredibly lame and i liked the first one
highlander 2, that counts as scifi, it did happen, who knows maybe we will meet again, not fucken likely
i can only think of four
You mean you could only think of three; there is no Highlander 2.
Ha. I think the sole pupose of *Highlander 2 *was to convince people that *Highlander 1 *was a good movie, which it really, really wasn’t.
This may have been funny originally. If it was though, it certainly isn’t any more. Highlander 2 existed and it was terrible. So did Star Trek V, (but it wasn’t terrible.)
Off the top of my head though, certainly missing some.
Highlander 2. Worst film I’ve ever seen
Battlefield Earth
Star Trek Insurrection
Babylon 5: Legend of the Rangers
Wing Commander
**Killdozer. **A bulldozer get posessed by alien life force and goes on a rampage. This might be fun to see again but I remember it (from a long, long time ago) as pretty awful.
Voyage to the Bottom of the Sea (not the TV series, though that was crap too) Dull and ridiculous. One repeated shot I seem to remember is you see a bunch of the protagonists sitting at the ENORMOUS window at the front of the deep sea***** sub, some of them smoking. I think they saved the world by setting fire to the Van Allen belts or something. Stupid.
**Highlander 2. **Haven’t seen the whole thing but I saw some of it while tripping and it was still too boring to hold my attention.
**Earth vs Flying Saucers. **Five minutes of Harryhausen fun embedded in hours and hours of tedious bollocks.
Ghosts of Mars. I think it may have had boobs in it at some point, otherwise all I can remember is thinking at the end that I’d like that hour and a half back please.
*****IIRC they enter the infamous Marianas Trench with something that looks like a greenhouse at the front of the boat.
I don’t have quite as negative an opinion of this one, but one of the elements I love the best is how quickly the crew (and some of the officers) comes to the brink of mutiny (aside from the mundane insubordination). 
BTW—I wasn’t able to find a clip of the most famous moment (“Imperial battleship…stop the flow of time!”), but I did dig up another classic Star Crash moment)
Makes Flash Gordon look like 2001. Both in technical realism, and general quality.
It’s okay - after they ran into some mines and the sub sprang a leak, they had a big wheel they could turn to make the leaks go away. I always loved that bit.
I haven’t seen Battlefield Earth and I actually liked Starship Troopers so…
- All three Star Wars prequels. During the pod race I genuinely caught myself thinking “I wish I was watching the lightcycle scene from Tron right now”. And The Stupid just kept snowballing. “I’m angry, therefore I’ll kill a room full of children!.” “Gosh, with our incredible technology we totally failed to notice Padme was having twins!” etc etc etc.
- Armageddon. You need to destroy the asteroid in the next 60 seconds to keep all life on Earth from being destroyed, so why not take 59 of them to make a mushy speech?
- Godzilla (the Matthew Broderick one). So many reasons.
The first one that came to mind was Zardoz.
Event Horizon, which seems to have been a horror flick disguised as a Sci Fi flick. It really brought the dumb.
Crime Zone
Deepstar Six
Highlander 2
I Come in Peace
Star Trek V
Alien
Plan 9 From Outer Space
The Matrix Reloaded
Space Mutiny
Battlefield Earth
Re Star Crash. It wasn’t all that bad, if you concentrated on the scenery.
Seriously, though, yes, Star Crash was bad.
So were :
Battlefield Earth
Highlander 2
Fortress (Hmm, two Christopher Lambert movies. might that be the start of a pattern ? Someone should investigate)
Deepstar Six
Space Trucker