I’m thinkin’ that would be The DreamTeam.
The movies I’ve given a ‘1’ at the imdb:
In general (but not always), if the film’s from before 1970, I saw it on MST3K. For many, I have only myself to blame, as my friend and I often intentionally seek out bad movies to rent. ‘Der Clown’ is probably the worst of the self-inflicted horrors.
Attack of the Giant Leeches (1959)
Battlefield Earth: A Saga of the Year 3000 (2000)
Beast of Yucca Flats, The (1961)
Beatniks, The (1960)
BJ and the Bear (1978) (TV)
Black Hole, The (1979)
Boxing Helena (1993)
Catching Trouble (1950)
Clown, Der (1996) (TV)
Creeping Terror, The (1964)
Curly Sue (1991)
Dancer in the Dark (2000) I may get flamed for this one, but I really couldn’t stand it.
Eegah (1962)
Faces of Death 4 (1990)
Fire Maidens From Outer Space (1956)
Folterkammer des Dr. Fu Man Chu, Die (1969)
Fugitive Alien (1986) (TV)
Going Ape! (1981) Tony Danza, Danny Devito and three ourangutans. You fill in the joke.
Goonies, The (1985)
Howard the Duck (1986)
Hudson Hawk (1991) Whenever my friend and I saw a hideously bad movie, we could always say “At least they didn’t sing.”
I Accuse My Parents (1945)
Injun Trouble (1938)
Inspector Gadget (1999)
Jungle Goddess (1948)
King Dinosaur (1955)
Lost Empire, The (1985)
Lost Idol, The (1990)
Maciste e la regina di Samar (1964) Released on MST3K as Hercules vs. The Moon Men
Mandingo (1975)
Manhunt in Space (1956) (TV)
Manos, the Hands of Fate (1966) Took me three tries before I could stay awake for through this one.
Master of Disguise, The (2002)
Miami Golem (1985) The name kinda says it all, doesn’t it?
Mighty Jack (1968) (TV)
Mitchell (1975)
Mr. B Natural (1957)
Nothing But Trouble (1991)
Oh, God! Book II (1980)
Outlaw of Gor (1989)
Phantom Soldiers (1987)
Pirate Movie, The (1982) Achieved the impressive feat of making Gilbert & Sullivan worse than it already was.
Popeye (1980) One of the few mainstream movies more painful than Hudson Hawk.
Rage (1966)
Ring of Terror (1962)
Rocket Attack, U.S.A. (1961)
Romeo + Juliet (1996) Moulin Rouge would be on this list, but I learned my lesson about Baz Luhrman from this piece of crap.
Santa Claus (1959) The horror… the horror…
Santa Claus Conquers the Martians (1964)
Saru no gundan (1987)
Shiberia chotokkyu (1996)
Showgirls (1995)
Skydivers, The (1963)
Stroker Ace (1983)
Sunchaser, The (1996)
Supergirl (1984)
Superman IV: The Quest for Peace (1987) Super-sucked.
Teen-Age Strangler (1965)
Things to Do in Denver When You’re Dead (1995) I know a lot of people love this one, but I just didn’t connect with it.
Undersea Kingdom (1936)
Very Brady Christmas, A (1988) (TV)
Movies I’ve walked out on:
Dirty Duck (the one made by Flo and Eddie of the Turtles – my wife and I thought it was based on the R. Crumb comics. BIG mistake!)
Solaris – the original. Boredom has a name. Its name is Solaris. I was so amazed they did a remake of it. I was not surprised that it tanked at the box office despite strong publicity efforts.
The worst I’ve encountered on cable is “Aftershock” a plotless Roger Corman melange of people running around an abandoned industrial plant, hitting and shooting each other. Even worse than his other stuff because there’s no drama, nakedness or well-realized fight scenes to relieve the tedium. Just more running and hitting.
Battle Royale- The Lord of the Flies movies were better and those kids didn’t even need pistols and rocket launchers and stuff to kill each other off. Battle Royale looked to me what ‘Reality’ shows are going to sink to in the next 5 years 
Beowulf- Starring Christopher Lambert. God this movie was so bad it was hysterical.
Ice Pirates- I’m surprised nobody mentioned this movie. Incredibly cheesy Star Wars/Alien knockoff with abysmal special effects. Thought the movie was hilarious, which made it redeeming. One of the terminals in the bridge of the ship has ‘space invaders’ playing. Another scene has a crew member idly watching the movie ROLLERBALL on a monitor 
OK all the above are bad… very bad in fact.
But the worst movie of all time is…
Lawn Mower Man 2
Even the special effects sucked. It looked like Tron but was made in the 90’s.
and the runner up?
StripTease with Demi Moore
How can a movie about strippers NOT be sexy? puh-lease
For me, it was Highlander II, but I’ve forgotten it by now, so Star Trek V replaces it.
William Shatner should not have been allowed any more creative control than saying his lines. We didn’t need Kirk, Spock and McCoy singing Row Row Row Your Boat around a campfire.
I hated all Highlander films. The first one is a horrible movie.
But not as bad as
Grease 2
I can’t even enjoy this for a cheese factor.
Supergirl
I saw this film for free and I was angry at the end of it. The’ve released a special edition with tons of extra footage. I can’t imagine that more screen time could make this any better.
Henry and June
Uggh
MonkeyBone. My Roommate brought this home as a pre-screener from the Rogers Video where he works. We were sooo glad it was free. Terrible film.
a bunch of odd Canadian Film Board messages from back in the 70’s and 80’s would probably get the nod if I could remember them. For some reason all the movies produced by CFB had non-endings that either left nothing resolved or made no sense at all.
Eventually, in my family, anytime a movie ended and we all reacted with “What? That’s the end??” one of us would always say, “What is this? A Canadian movie?”
Dem’s der fightin’ wurds.
The first was excellent, but the second was a horrible, horrible movie that, even while just sitting here thinking about it, makes my ears bleed.
“Crossroads” came close to unseating my all time least favorite, “The Frog People of Venus.”
These are leg chewers. (ie: you would chew your foot off to get out of one.)
Tris
Speaking of leg chewers, Coyote Ugly was one awful movie.
Jberto mentioned Sergeant Pepper’s Lonely Heart’s Club Band. This is easily the worst thing I have ever seen committed to celluloid. But it’s not just bad, it’s fascinatingly bad. So much so that I find myself recommending it to people. “You have to see it,” I plead. “I need to be able to share this with someone.” But nobody will listen. I think they hear what I’m saying and think “Yeah, that must be a really bad movie,” but I don’t think they appreciate how truly bad it is.
Everyone else seems to be citing movies that a lot of people would agree are bad. I’ll take on some sacred cows:
Pulp Fiction. The worst, most disgusting movie I’ve ever seen in my life (and I’ve seen I spit on your Grave; I’d rather watch that again than watch Pulp Fiction again).
L.A. Confidential. Forgettable plot filled with nothing but completely morally bankrupt characters; how could anyone care what happens to any of those people?
Saving Private Ryan. The first half an hour was movie-making at it’s finest. The middle was just a snooze. The last half an hour was totally revolting and so overshadows the first part that it turns the entire movie into trash.
Forrest Gump. Dumb movie about a dumb guy, and everyone he ever loves (except one) DIES by the end of the movie!
Ok modifying my list
Star Trek: Nemesis
OK for most people - Awful for Trekkies
It just couldn’t decide what movie it was. First ST:TNG - then oh look a garbage chute like place to escape - Star Wars. Then metal grating obscuring bad guy - Hunt for Red October. Then fighting bad guy leaning over REALLY big shaft in middle of ship - Empire Strikes Back. …channels several bad B sci-fi movies… then finishing it off? Superman.
Very disappointing
let me see…
~Plan Nine From Outer Space
~The Adventures of Bukaroo Banzai
~Soylent Green (SOYLENT GREEN IS PEOPLLLLLLLLLLLLLLLLLLLLE!!! …sorry, just had to)
~Anaconda (I had nothing to do one night and it was on t.v.)
The Musketeer - if you saw it, you’ll know why.
You’ll find that “morally bankrupt” characters are some of the most likeable in the universe. Witness the popularity of the likes of Boba Fett.
Eight Crazy Nights with Adam Sandler. Just a really bad movie. My friends liked it though, which makes me think maybe I’m smarter than the average person my age (my age being 15).
Forrest Gump was a bad movie and was bad for movies. Every scene seemed to last just as long as the classic rock song that was being played in the back(fore)ground. Turned out to be contagious… most of the movies these days seem like an interconnected series of rock videos.
“Popular” and “likeable” have no relation to each other. Besides, I don’t care what’s popular. Obviously, the movies I cited were emensely popular. That many other people found them enjoyable doesn’t change that I thought they stunk.