The only one I can think of is Prizzi’s Honour only because I wanted to leave but assumed my wife was enjoying it. She wanted to leave but whenever she glanced at me I was watching so she assumed I was enjoying it.
I recall an interview with Peter Sellers in which he was asked, “If you had your life to live over again what would you do differently?” He replied, “I wouldn’t go and see The Magus.”
Off the top of my head, Closer, Eyes Wide Shut, Shark Tale, Poseidon (though some of the deaths were nice), Queen of the Damned and the last two Matrices. 
The Virgin Suicides wasn’t quite as bad, but it came close. Were I not so picky about which movies I see in the first place (when I’m not dragged), my list would likely be much, much longer. I’m just guessing that Moulin Rouge, Chicago, Alexander and Eternal Sunshine would be on that list.
Ah, and once we rented some movie about a man who loves a realdoll-type doll - “Love Object” or something like that - which was bad enough to make us turn it off halfway through. I would probably never walk out of the theatre, though. I mean, if Hostel had continued in the same vein with which it began, I think it would win my worst movie of all time award. As it turned out, it only rated a “pretty terrible” with me by the end.
Omega Doom with Rutger Hauer. A movie so unbelievably dull and terrible, I don’t think it could even be MST3K’ed.
I’ve actually never walked out of a movie theater over a bad movie before. I figured I paid the money, I’m getting all the suck I can outta of it!
now, DVD’s thats anothe story…
Brothers Grimm - Worst execution of a good idea… EVER
Ultraviolet - Ugggggggg
House of Dead - Double uggggggg
AI - I A dummy for renting this at all
Pink Panther (Steve Martin) - this was so bad it actually impacted good childhood memories of the originial movies.
Doogal - My eyes, they burn…
Driving Miss Daisy - Classic my ass… Drive me to get some coffee before this movie puts me to sleep…
2001 A space odyessy - Blah, blah, blah… Not everything in a movie should symbolize something else. Sometimes it should just be about the movie.
Gridiron Gang - The Rock should have to go to an actual prison after making this movie, it was a crime.
Bah, my head hurts just thinking of these movies!
I rented Orlando after hearing lots of hullaballoo about it and how EDGY OMG it was.
It wasn’t terrible, but I didn’t see the awesomeness of it.
Now, actively terrible movies. Hmm. Probably the second Zorro movie that Banderas made. My coworker and I wandered out wanting our two hours back – and this is a guy who liked Ultraviolet and Ghost Rider.
I saw Ultraviolet in the theater. I have the horrible suspicion that not being able to hear what anyone was saying made the experience a tad more bearable. 
The Color Purple - I didn’t know it was possible to care that little about any of the characters in a movie…but I did it.
Bad Santa - I can honestly say that this is the only movie I’ve ever walked out of. How it got made and why it was ever shown is incomprehensible to me.
I, on the other hand, cried at the end of the movie a little. I was so touched by Billy Bob’s character truly caring about the fat kid.
And as for my addition to the list, I can proudly say:
ALL THREE Lord of the Rings movies. I want my 9 hours back.
Well I sort of liked Dogville and Gerry, and being on a first date and watching the Dark Crystal - how can that be a waste of time - unless of course the date was spent watching the film and getting no closer to your true goal.
My votes go to A Home at the End of the World. A film where Mr Farrel once again manages to induce feelings of dispisement towards a character that we are supposed to feel sympathy or some such towards. In fact the whole cast gets in on that sort of action, I can’t think of any character that I actually liked. Utter waste of celluloid or whatever todays media is.
There was another one about an American and British academics following the life of some edwardian poet and his love life. Can’t remember, but toss, pure unadulterated chunky flecked toss.
The Matrix. What a waste of time.
Some of the ones I saw recently travelling to and from Rome weren’t great (Marie Antionette; The Queen) but I was stuck on the aeroplane anyway so I suppose it wasn’t really “lost” time.
Alone in the Dark
Here is the review I wrote in Yahoo! Movies
Home Fries…dear Lord that was terrible…got dragged to it by my ex.
The first one to come to mind is Scooby Doo 2. Now, I get that I’m a bit older than the target audience, but what a pile of crap. The only reason I didn’t walk out was I wasn’t sure if my friend wanted to (he did), and neither of us said anything 'til afterwards.
Then there’s Don’t Look In The Basement. Right, I spent the entire movie wondering when a basement would become relevant. After awhile that was why I kept watching. I just HAD to see if there’d actually be a basement either walked into, looked in, or spoken of. Nope. I can’t think of any redeeming qualities.
For my borderline vote, I say The Cook, The Thief, His Wife and Her Lover. I mainly watched that because of it’s reputation. I heard that it was so gruesome and disgusting that people walked out within the first half! Being a horror film junkie, I couldn’t pass it up. It was interesting in some respects (the color-changing wardrobe was fantastic), and the last 10 minutes were great (and truly disgusting), but most of the movie was just dull. I was rooting for that singing kid to die early.
I’ve seen a lot of poopers lately.
Pom Poko. Probably the most boring movie I’ve ever seen. No, wait - that was The Queen.
I agree about The Brothers Grimm being a terrible execution of a great idea.
Some others:
Sin City
A History of Violence
For Your Consideration
The Illusionist
Marie Antoinette
La Moustache
Last Tango in Paris
Match Point
The Witches of Eastwick
Corpse Bride
Charlie and the Chocolate Factory
Broken Flowers
All of the above are movies I wish I’d turned off but for some reason kept watching until the bitter end. (By the way, I love being able to look at my rental history on Netflix.) As for movies I’ve actually turned off:
The Wedding Date
Saw II (but that was after watching only one minute and realizing that I just don’t ever want to watch that kind of movie again)
Bounce
Man of La Mancha with Peter O’Toole
Fiddler on the Roof
Yentl
Mostly it’s movies I had absolutely no interest in but went because a friend wanted to see it. I no longer do that; dinner is great but I ain’t wastin’ 2 hours of my life on something I don’t want to see.
Meet the Parents (I hate misunderstanding type movies, I left and watched another movie waiting for my friends)
Gone in 60 Seconds (at one point, I was actually more interested in watching the dust motes in the projector beam than what was on screen)
The Incredible Hulk (how bad could it be? Dull, dull, dull)
That Jim Carey movie where he has God’s powers (A friend called me up sobbing because her boyfriend had accused her of covering something up because she was being nice by buying tickets for this movie. So I grit my teeth and suffered through it. I still haven’t forgiven the boyfriend.)
I’ll second Highlander II. I rented it from Blockbuster, just to find out if it was really as bad as everyone says it is. It wasn’t. It was worse. High school plays have higher production values and better acting than that cinematic abomination. Not only do I want those two hours back (or however long it was) I’d like my three dollars back, too. One good thing came out of that experience, however. Whenever a Star Trek fan insists that Star Trek V doesn’t exist, I can confidently think to myself, “You whiny little snob. You have no idea what a bad movie really is.” 
Recently, I went to see Epic Movie. This film holds the honor of being the only movie I’ve ever walked out of. I don’t know what I was expecting, exactly, but that movie was sorely disappointing. The humor was very crude, very dumb, and very mean-spirited. After about 30 minutes, I looked at my girlfriend and said, “Let’s go back to my place and watch TV, OK?” and she said, “Yeah, let’s go.” The Travel Channel’s show about ghost investigators proved to be far more entertaining.
Midnight in the Garden of Good and Evil.
Literally a snoozefest, as I slept through most of it. Hey, I guess I DID get my time back!
Hey, at least it’s a good cure for insomnia. Seriously, I was really disappointed, having read and enjoyed the book.
Another vote for Alexander. I’ve never looked forward to a movie so much that turned out to be so utterly awful. My roommates-at-the-time and I are all huge ancient history buffs. Alexander’s story would make an awesome epic movie, and we were really excited. And then it was. . . it was. . . Man, you mention it to any of us now and we’ll still grumble.
We got Date Movie from netflix and it was a gross & crude waste of a postage stamp, but these problems are solved by the buttons on the remote. I still want my time back for Alexander. I want the anticipation time back, too, damnit. I don’t want to have looked forward to it. Learned my lesson about opening night/not reading reviews, though.
(Yes, yes, 300 and Troy ran roughshod over history. I was too busy drooling at all the muscles*)
*Contrary to popular assumption, I’m a chick.
Dune. I was 14. I didn’t understand. Castaway. I was praying for something to eat him so I could go home. And Braveheart. I was 8 months pregnant and after the second false ending I stood up and yelled “Just DIE Wallace!” Which got me escorted out, and I was crying because I was hormonal and uncomfortable, and it was a bloody horrible movie.
Sorry to hear that, but this is still the funniest thing I’ve read all day