You can't expect Hollywood screenwriters to think of every movie. They gotta come from other sources, and, when the venerable, traditional sources of film's raw material (TV, Novels, Plays, Older Movies) runs out, filmmakers turn to other raw materials.
Below are the most egregious failures in film adaptations in the history of ever. It's personal, not comprehensive, so feel free to add your own in our comments section!
Silent Hill (Based on the videogames)
Step 1: Take a beloved franchise.
Step 2: Take the setting of the game and make everything else up.
Step 3: Throw in Pyramid Head.
This movie is an Epic Fail because it had so much potential. It even had a great start to it, but it’s like the film switched directors half-way through. The ending contained a sequence that basically tried to explain what was going on in a few minutes and I’m not even sure they knew what what going on in this terrible adaptation.
Garbage Pail Kids Movie (Adapted from the collectible cards)
I’ve been actively pursuing awful films since the days of VHS, trolling dusty video stores and public access channels for the very worst of the worst of moviedom. I’ve discovered some unheralded masterpieces masquerading as low budget exploitation (Christmas Evil, The Stepfather) but mostly pure schlock (Sorority Girls Revenge, Santa Claus Conquers the Martians). Schlock or not, there’s something to love in all films, whether it’s the weird enthusiasm and mid-western “Let’s put on a show!” vibe of Cornman: American Vegetable Hero or the so-unexpectedly-over-the-top-and-ridiculous-it’s-infectious vibe of Death Wish 5. I’ve only found a single film in my lifetime of bad-movie watching that has absolutely no redeeming qualities at all, and that film is The Garbage Pail Kids Movie.
GPK is the first feature filmed based on collectible cards with drawings of horrible children on them, which is epically fail in itself. Who could have possibly believed that a briefly popular trend in schoolyards would make a viable film franchise? Sure, you could see a parent begrudgingly shelling out a couple quarters for a pack of cards with pictures of a vomiting freakshow (Valerie Vomit) or a flatulent punk (Windy Winston), but expecting that parent to sit through 90 minutes of the Kids on a 40-foot screen is something entirely different. But even if little Dylan managed to wheedle his parents into taking him to mall to check it out, he's much more likely to be plagued with a lifetime of nightmares than be mildly entertained.
Garbage Pail Kids' architects seem not to have noticed that the movie is a vision of living hell. While the cards were kind of funny in the schoolyard, seeing stylized, cutesy drawings of grotesques is not the same as watching their huge, misshapen heads actually interacting in a realistic setting--considering a physical existence for the titular abominations is truly twisted, and the fact that the filmmakers seem blithely unconcerned makes for a disjointed, surrealistic hell-ride.
The Garbage Pail kids are abominations that should not be allowed to live. For example, Ali Gator (har har), one of the main Garbage Pail Kids (who is not actually a kid but rather an Alligator) enjoys biting people’s toes off. He wears a Hawaiian shirt in an attempt to appear lovable, but it doesn’t work. When he walks around expressing his one desire to eat peoples feet, it's not funny or gross, it's just ...wrong. Ali is an animal that wants to bite people’s feet apart, for God's sake. Kill it! He and his paper mache, farting, pustulent brethren serve only to horrify and disgust in a truly soul destroying way.
It's way too scary for the intended audience of children, but while the creep factor is too frightening for the kiddies, the sub-moron script is just too dumb for any but the most developmentally disabled child.
But the most horrifying thing in the movie is Mackenzie Astin, an 80s kid actor who performs as if his overbearing stage mother is standing right off-screen with a cattle prod. He cries throughout the movie and has some unspeakable romance with a lady in Spandex with teased hair and too much eye shadow. Then there's the plot...
...I'm sorry, I can’t write about this anymore. While I could keep ranting all day, it hurts my mind to think about this movie. But it's epically fail. Epically, I tells ya!
Fast Food Nation (Adapted from the Book)
Sure, it's no big surprise that the adaptation of a best-selling book was a disappointment at the box office. That stuff happens all the time. But wasn't some John Grisham legal thriller or Stephen King shockfest. No, this book was different. Fast Food Nation was an expose, akin to Upton Sinclair's The Jungle, where the country's fast food industry was the focus rather than the meat industry of Chicago. Director Richard Linklater tried to turn this industrial expose into series of narrative vignettes, but the movie never really took off. The fail here was not in the filmmaking per say, or in the writing of the source material, but simply in the selection of source material. Not everything can translate to narrative film, and Fast Food Nation is exactly that. Noble effort, but Epic Fail.
Superstar: Dare to Dream (Adapted from Molly Shannon's SNL Mary Catherine-Gallagher character.)
It's one thing to create a one-dimensional wacky character for an SNL sketch. It's another to repeatedly pound that character into the show and the national consciousness in a relentless metronome-like pattern for years on end. Add to that the fact that this two-joke pony (smelling her armpits and jumping through a wall) was eventually adapted for one of the worst movies of all time and you can understand why this failed character is so hated. Not to mention the troves of girls getting into comedy that imitated her in an effort to outfit their comedy toolbelt, only to find crickets in the improv audition room. I want to shoot this character in the face a hundred times for representing everything lame in comedy.
Also, please read this review of Superstar from "Teri." The font choice alone is hilarious.
Monopoly: The Movie (adapted from the boardgame)
Yes, this is real, and yes, Sir Ridley Scott has been rumored to be the director.
What would you have in a movie based on the board game Monopoly? I’m guessing at some point, someone will go to jail, and someone will come and just visit them. Obviously, there will be a scene in which someone wins second place in a beauty pageant, and is given $10. Also, how will they deal with passing Go? This is literally incomprehensible as a film project. Still, they better base it in Atlantic City, New Jersey, or I’m going to bust some f***ing skulls.