Only one–the first Tomb Raider movie. My sister and I went to see it. About partway through, we were both ready to leave. And she was maybe 13 at the time.
I once picked up a copy of the movie Fate from the Blockbuster. It had Phillip Michael Thomas in it! I love him! Then about 20 minutes in I’m trying to figure out where Phillip Michael Thomas is when it dawns on me that I don’t actually like Phillip Michael Thomas, I am a huge fan of Phillip Seymour Hoffman. I confused my three-name Phillips. I turned it off at that point and returned it to the video store.
I so rarely go to the cinema due to cost, time and childcare issues so I’ve never walked out, although if I hadn’t been with someone else whom I had agreed could pick the movie I would have sprinted out of Tango and Cash. Really bad.
I rented Bonfire of the Vanities, watched ten minutes, stopped it, rewound it, ejected it and immediately drove it back to the store. I didn’t even want it in the house.
There are also a lot of movies I’ve watched at home and ended up fast forwarding through the majority of, like all three of the **Star Wars **prequels or Mel Brooks’ Silent Movie. So technically I watched them - I just saved a few hours of my life by zipping through the stupid parts.
Haven’t walked out on a movie many times, but one that comes to mind was **Leaving Las Vegas **- my companion was just disgusted at the very premise of the movie and basically was going to be such an unpleasant pill if he was forced to sit through a (make-believe!) (NOT REAL LIFE!) movie that depicted someone choosing to drink themselves to death - that I finally asked him if he’d like to leave, and he jumped out of his seat like there was a fire underneath it.
A couple of years later, I saw the rest of it on cable, and while it’s not my favorite movie ever, it was good acting. Sometimes, though, you can’t enjoy a movie, or a meal, etc., if the other person is hell-bent on NOT enjoying it.
Movies I wish I’d walked out of - Dark City, Dr. T and the Women, Weekend at Bernie’s 2, Batman & Robin, and just about anything penned by Quentin Tarantino or Robert Rodriguez. Grindhouse, anyone? 
I’ve only ever walked out of one movie - I don’t go to them very often. It was “Something New”, and we left after I turned to my husband and, not looking at the screen, told him what was happening/going to happen. Going hiking? Ok, now its going to start raining. They’ll hide out under a tree and start kissing, then it will cut to them kissing in her house, knocking over furniture. When her big vase bit it, we left.
I wish I walked out of Star Wars Ep. 1. EP 2 was passable because of yoda (“Around the survivors a perimeter create”), but hayden makes me want to vomit whenever he was on screen. My wife dragged me to see 3, and it was as bad as I thought it would be.
The aptly named Misery, with James Caan & some horrible no-name actress who started getting lots of roles after that.
Was there with friends. Got sick of it & went & watched Edward Scissorhands by myself. To this day I [del]think[/del] know I made the right choice.
The only movie I’ve ever walked out on was Emanuelle, in part because the print that was running was butchered and had other movies actually intercut with it.
Movuies I should have walked out on:
Gas and The Trouble with Spies – both films insisted upon by the friends I was with at the time, because they had Donald Sutherland in them. These people clearly didn’t know that Sutherland will do anything for enough money.
My Dinner with Andre – i liked Wallace Shawn (who wrote and starred), even before he was a household name, but for the life of me I don’t get this one. I started falling asleep.
Jake Speed – 1980s action-hero wannabee.
Two have come close:
Blair Witch ('cos I had motion sickness watching it)
Royal Tenenbaums - “funniest comedy of the year”, my arse… load of achingly hip, self-indulgent wank IMO.
edit: 79% on rotten tomatoes!! Unbelievable.
I never walk out of movies. I do mentally check out on some, though. The two that come to mind:
Natural Born Killers. A horrific mess of a movie, just violence for the sake of violence, and an embarrassment (or it should be) to all involved.
Little Nicky. I got dragged to see this one by a friend who just lurrrrrves her some Adam Sandler. Whooooeeeeee, it was bad. Total waste of time and money.
This line could be used to describe every single one of Wes Anderson’s films. He’s rubbish.
Back in 8th grade, my friend and I did the classic buying ticket to PG-13 movie and sneak into R. So, technically I walked out of some Disney dog movie to see Silence of the Lambs. In high school, a friend forced a group of us to walk out of Pulp Fiction. I walked out of Francis Ford Coppola’s Dracula. The werewolf sex hit my limit of bad so adios.
I wish I had walked out of 2010’s Clash of the Titans. It was so awful on every level. Chyron’s ferry over Styx looked like the kind of ferry that can carry CARS. Why so literal dopes? Also I wish I had walked out of that Vampire’s Apprentice movie. The commercials made it look funny plus I love John C. Reilly.
I walked out on Footloose when it first came out in theaters, but I really should have known better.
Movies I rented and didn’t watch all the way through: Sid and Nancy and Gone Baby Gone. GBG was based on a book by the same author as Mystic River and I liked that movie, but in this one I found it difficult to follow the plot. Morgan Freeman was in it too, and it was around this time I decided I had seen enough Morgan Freeman to last me 3 lifetimes.
I didn’t care for Napolean Dynomite except for his final dance scene.
Night at the Museum could of worked if Ben Stiller wasn’t in it. Why is Ben Stiller in movies? WTF? Ever see his mother Anne Meara? I’d like to hit her with a truck. So would Frank Costanza!
Movies on cable I couldn’t finish:
Napoleon Dynamite
The English Patient – to quote Roger Ebert (though not about this one) I hated, hated, hated this movie.
Cool World - I didn’t walk out, but thought about it
I very seriously considered walking out on Catwoman. And I was on an airplane.
Walked out of Battlefied Earth within 15 minutes, which I’ve always heard as the cut off for being able to demand your money back. No idea why. Se we tried it. The theater acknowledged that they adhered to that policy but then argued that they counted the previews as part of the feature. I got a little pissy since there’s 15 minutes of previews nowadays so if they are going to honor that policy at all, it needs to be 15 minutes of the feature.
We got our money back.
After sitting through Spiderman I remarked to my girlfriend, “I would have walked out of that if you weren’t with me.”
“I only stayed because I thought YOU wanted to see it to the end!”
I don’t think I’ve ever walked out on one, but when I went to see the John Waters film A Dirty Shame, a couple walked out during the water bottle scene. I wanted to ask them what they thought they were coming to see - it was a John Waters flick rated NC-17 at the local art theater for chrissakes - but instead just sat and enjoyed the movie. (Not his best, but fun.)