Aladdin (2019): Jafar's genie form looked outright diabolical in the animated version. In live action? He just gets bigger. Audiences actually seemed more freaked out by Will Smith's Unintentional Uncanny Valley genie.
The "crab walk" Deleted Scene in Alien. It features the titular alien attracting attention to Lambert, the film's Hysterical Woman, with its very long tail. The alien is menacingly sitting on the ground, blending in with the environment... and then proceeds to awkwardly scoot across the floor to Lambert and showcase what is obviously just a man in a suit. The scene is just so laughably odd and off-putting, even if that was the intention in the first place.
Ultron's moveable humanoid face throughout Avengers: Age of Ultron. For some, it's just not as scary compared to the other images that closely resemble the twisted metal abomination he's based on. Also, the fact that Ultron appears to have teeth despite being a robot with no seeming need for human food. Ultron's penchant for snappy one-liners utterly ruins his scary factor. Compare to his first appearance, where he can barely talk.
Beginning of the End featured giant mutant grasshoppers played by regular-sized grasshoppers crawling across pictures of the Chicago skyline.
Blood Freak: The idea of a vampire (or vampire wannabe) feeding on the blood of drug addicts could make for a genuinely good horror story, but the visibly low budget, said vampire's ridiculous appearance as a man in a cheap turkey mask, and the awkwardly shoehorned-in religious message make it impossible to take any of it seriously.
The "bat suit" in Bram Stoker's Dracula. Apparently, it was added because Gary Oldman didn't feel he could be scary enough for that scene. Ironic, since he was a lot scarier without the dippy rubber suit.
Listen to the noise the parasites in Cloverfield make. It sounds like Donald Duck, for God's sake. Or maybe Yoshi. Fortunately, Clover's roar more than made up for the silly parasite chittering.
A lot of other horror/comedy movies just aren't scary because, no matter how much blood, gore, and death the sadistically evil villain leaves in his wake, he's so absurdly funny that you're laughing too much to take him seriously. For example, there's Leprechaun (leprechauns aren't scary, no matter how ugly they are, especially when they're afraid of four-leaf clovers), Santa's Slay (a Bad Santa is funny, not scary), Jack Frost (1997) (you can have this guy rape a woman in the shower if you want, but the fact that he's a snowman still makes it hard to take him seriously), and The Gingerdead Man. (This guy is a living gingerbread cookie! How is anyone supposed to be scared of that?)
In The Creeping Terror, the eponymous creeping terror was an alien who ate things to study their biology (or something like that), and it was clearly supposed to strike fear in the viewers, but only made them giggle. It resembled a large carpet slug that shuffled along slowly, and its victims, instead of running away like most sensible people would have done, stood there and screamed while the creature ate them. The costume was such that the victims actually had to crawl into the hole in the front that was supposed to be its mouth.
In a scene near the end of the film version of The Day of the Triffids, the characters shelter at the top of a lighthouse while a Triffid's tendril crawls up the stairs towards them. Unfortunately, it's quite obvious that the tendril is a sock puppet. Also, the Triffids themselves were basically giant sunflowers. SUNFLOWERS.
Another example from Wes Craven that ended up this way due to Executive Meddling is Deadly Friend, in large part because it wasn't even originally intended to be a horror film, but the studio wouldn't allow Craven to film it any other way. Most infamously, the scene where Samantha obliterates an old woman's head with a basketball is played for horror value, but it's so ridiculously filmed and looks so unconvincing that it's impossible to find it horrifying in the slightest. Even worse in this regard is the Gainax Ending where Samantha transforms into a robot and strangles Paul to death.
The 1931 version of Dracula contains two misguided attempts at symbolism: a close-up shot of a Jerusalem cricket (which looks a lot like a giant bee) crawling out of a coffin and a "giant rat," played by an opossum. In the Spanish version of the film, the "giant rat" falls off of the ledge it is walking on during the shot. And then there are the armadillos and the "terrifying" rubber bats on strings in that and so many other early Dracula films.
The scene in Drag Me to Hell wherein the goat is possessed by the malevolent spirit and the lamia dances. Although, being directed by Sam Raimi, this was probably the goal.
Eight Legged Freaks, though played for Black Humor, had a potentially very scary premise: realistic-looking giant spiders are pretty horrifying by themselves, but the decision to give the spiders all sorts of "wacky" jabbering noises as they run amok utterly wrecks the terror for the most part. There are some scenes that aren't played for laughs that manage to be genuinely frightening, but they are rare. There is a memorable scene where a spider jumps on the stuffed head of a moose, only to take a bite and look visibly annoyed at the taste. Though the shot of a truly gigantic tarantula moseying through a parking lot to a sinister, minor-key riff of "The Incey Wincey Spider" can be rather effective.
More or less the entirety of Exorcist II: The Heretic - quite infamously, given that it's the sequel to what's often considered the scariest movie ever. Highlights include a goofy "mind synchronizer" device, Reagan suffering an attack during a jazzy tapdancing performance, reams of nonsensical pseudo-metaphysical exposition, and James Earl Jones dressed up as a giant locust, spitting a leopard from his mouth.
The Final Destination series usually thrives on Paranoia Fuel, taking ordinary situations and turning them deadly in rather unexpected, but at least plausible manners. However, the more implausible deaths tend to have the opposite effect, and either has you rolling your eyes or laughing hysterically. This was especially bad in the third and fourth films, where both of them include the overuse of illogical domino effects.
The 1989 horror movie Gnaw: Food of the Gods II has a scene in which giant rats attack a swimming competition. The cheesy special effects, however, kills any shred of horror from the scene. The intercutting shots of panicked people in a normal sized competition pool with shots of ordinary-sized rats walking around and splashing in an obvious miniature pool had no credibility whatsoever.
While the first movie in the series is pretty good, all of the other films of the franchise fit this trope to a T. There is something strangely comedic about seeing a guy in a hockey mask wander around the woods like he's lost, machete or no machete.
The bits where Mrs. Voorhees assumes the character of Jason and starts saying things like "Kill her, Mommy!"
The production team and writers seemed to invoke this trope willingly for Jason X when he's presented with a hologram of 2 busty, naked co-eds saying that they love partying and having unprotected sex. Hilarity Ensues. After a cut-back to the crew of the ship.
Ghostbusters has this trope as the whole premise of the franchise: there are horrific and powerful forces lurking in the shadows ready to do their evil at any time. However, they can be studied scientifically by learned experts, who in turn can develop effective and easy to use weapons and countermeasures those eldritch menaces will never see coming. In short, if you have the knowledge, the tools and the courage to face these supernatural entities of your darkest nightmares, they will have real reasons to fear you!
The Happening could, at one point, have been a suspenseful horror with a strong mystery element. Poor acting and the ridiculousness of the premise scuttle any chances of that, however. It's a tough ask to find walking around open, grassy fields in sunshine scary. It's a bigger ask to buy that some people nevertheless manage to get run over by harvesters.
The '80s horror film House has Sandywitch, a disgusting, nightmarish monster that attacks and tries to kill main hero Roger Cobb. But any pretenses of it being scary quickly fade when it speaks, as it talks in a high-pitched chipmunk voice.
The Invasion suffers many moments like this. For one, Nicole Kidman's character searches for the term my son is not my son on Google with no quotation marks. In another scene, many people are avoiding showing emotion to avoid the body snatchers. They tell the protagonist not to show emotion, then one of them snaps. The entire group, minus the protagonist, then fails to escape, even though nothing was stopping them beyond fear of a railway line (the alternative being captured by monsters and, for all they know, killed). In early scenes, the sense of paranoia is ruined when groups of people who very blatantly have something wrong with them are roaming around, long before anything being wrong with them is introduced as a concept.
This movie avoids calling itself a horror movie (a trait which, in horror stories, is associated with being made by people thinking their movies are "too good" for the horror genre). It's the only adaptation of the source story to replace the pod aliens with drink-infecting chemicals. Yep, it almost screams "never mind the shoddy writing, we've got rape imagery! Everyone's going to take us seriously now!"
"Mrs Kersh" from It: Chapter Two was fairly creepy when she was assuming the form of an old lady. Then she goes on the attack and transforms into... this.
Most of shark attack scenes in Jaws are terrifying since you don't actually see the shark. Then when the shark does appear in the end, it looks so fake that it becomes laughable. Even when the film was being made, Steven Spielberg felt the shark looked too phony, resulting in the Nothing Is Scarier approach. Spoofed by Marty McFly in Back to the Future Part II when the future's 3D Jaws sequel: "Eh, Shark still looks fake."
The original King Kong (1933) was released as a very frightening horror movie and was effective as such for many years. There were people fainting in the audience when it was first shown. Advanced effects have made us jaded. The version from 1976 has aged even worse, mostly because it doesn't even try to have Kong move like anything but a guy shuffling around in a gorilla suit.
The movie Link from 1986 is about a chimpanzee called Link who goes on a rampage killing people. While that does sound like a pretty neat concept for a horror film, it is ruined by several things, the first problem being he's dressed up in a butler's outfit, making him look rather silly and not very threatening, and the second biggest problem is that he's played by an Orangutan, something that the filmmakers tried (and failed) to hide by shaving the Orangutan's fur shorter, then dying it black, even though anyone with a brain can easily tell that Orangutans and Chimps physically look nothing alike, making the character look even more ridiculous and hard to take seriously, especially considering that Orangutans aren't particularly scary. To make things more jarring, they already had actual chimps used in the movie, leaving one to wonder why they couldn't just use a chimp to play Link instead of a Orangutan poorly disguised as one. The end result is unintentional comedy from start to finish.
The Lost World: Jurassic Park had the velociraptors suffer badly from this trope. Honest Trailers noted it, and dubbed Yakkity Sax over the scene where a raptor chases Malcom around an abandoned laboratory to highly how far the predators had fallen as it continually fails to catch a middle-aged mathmatician due to repeated pratfalls. And then a teenage girl manages to kill a velociraptor with gymnastics.
Mary Poppins has a nightmarish sequence when the Banks children flee their father's bank after accidentally throwing it into chaos. In their panic, they wander into the East End slums, dodging various frightening people until it climaxes with them colliding with a dark man seeming about to abduct them. However, when that dark man turns out to be their dear trusted friend, Bert, the whole mood instantly lightens with the audience knowing the children are in safe hands now.
The Monster of Piedras Blancas initially just shows glimpses of its title monster, and when its face is finally shown, it is inexplicably vomiting water at the same time.
Muppet Treasure Island makes no attempt to soften the numerous deaths and murders from its source material... and gets away with that by adding generous amounts of this. The fearsome Captain Flint, for example, is shown at the beginning murdering fifteen of his own crew to keep his treasure a secret. Later, Long John Silver laughs over Flint's chosen signpost of two dead bodies on the path to the treasure. And finally... we find out that Flint once dated Benjamina Gunn...who is played by Miss Piggy. Who complains that he was co-dependent.
Night of the Lepus is about giant rampaging killer rabbits... which are played either by cute little bunnies on a scale-model set, or people wearing garish rabbit suits. Yes, it's as hilariously awful as it sounds. Here. The saddest part is that the portions of the movie where the rabbits aren't on screen are actually pretty decent, and the miniature work is, for the most part, very good. It's just that, well, you've seen the clip. One instance of miniature work that isn't good is the down-the-empty street shot... with the 'giant killer stagehand' stepping off to the side.
Nosferatu: in the opening scenes, the villagers claim a werewolf roams through the forest at night. The atmosphere is really creepy and the audience wonders what this creature will look like. When the protagonist goes to sleep the camera shows a wolf-like creature walking in the forest, but it's clearly not a werewolf, left alone a wolf, but a striped hyena! And it's strange to downright ridiculous that this animal is walking around in Transylvania, Romania. This is one that was Fair for Its Day, as a hyena would have a been a much more obscure animal than it is now to European viewers, and appeared almost wolf-like but not quite, befitting the appearance of a werewolf.
Despite its potentially creepy premise,note college girls are hunted down by a cult masquerading as a fraternity many viewers felt Black Christmas (2019) rarely managed to pull off genuine horror and was even unintentionally funny at times. Most of the "scary" moments come in the form of cheap Jump Scares you can see coming from a mile off and the more violent scenes are heavily (and awkwardly) edited, which undercuts much of the tension. The big twist that the killers are being mind-controlled and given preternatural strength/endurance by magic black goo was also widely found too silly and outlandish, given the movie's attempt at a serious tone.
The 1925 version of The Phantom of the Opera appeared to have passed the test of time when it comes to this. Although reactions may not be as extreme today, the unmasking scene will still make many people jump in surprise. It even has the ever creepy uplighting technique. Unfortunately, when the Phantom jumps up and points directly at Christine after the unmasking, things that were once considered scary turn hilarious... at least if you're a fan of Family Guy, in which the Phantom's iconic scene was adapted for the Evil Monkey. Otherwise, the Phantom is still pretty damn petrifying.
The title character from Robot Monster (pictured above) was a guy in a gorilla suit. And a diver's helmet.
The creature from Roger Corman's Creature from the Haunted Sea (1961) is one of the goofiest looking monsters in the history of cinema— though considering the movie's supposed to be a comedy this may be intentional.
Signs is one of the more infamous cases. The direction surrounding the aliens is genuinely creepy, but by the end of the movie, you realize that you were cowering in fear of a monster with a very unoriginal design, is barely stronger than a normal human, treat a garden hose like a flamethrower and have trouble with pantry doors.
There is one part of the video-game-to-film adaptation of Silent Hill in which the Creepy Child bursts into flame and says "Look...I'm burning." Owing to how subjective this trope is, you either were creeped out by it or laughed your head off.
The Snowman is a film about a serial killer whose Calling Card is leaving a snowman next to his victims, with a frowny face. The film tries to play this as a sign of him being a Psychopathic Manchild, but it really doesn't work.
The undead Sammi Curr in Trick or Treat is an electric ghost, whose weakness is water. Fine enough, but when your movie's villain is shown being hurt by having his foot stuck in a toilet, he loses all credibility as a threat.
Werewolf (1996) had a monster that changed its look throughout the film. One of which being the producer's own pet dog. Yuri's hair was scarier than the Werewolves.
Wes Craven's Cursed was a good example of this trope, where the scenes meant to be scary were downright funny, and the scenes meant to be funny were downright cheesy. From the predictable plot to the bad acting, to the cheesy dialogue, this movie has it all. Strange how a film intended to reinvent the werewolf genre ends up falling back on every single Hollywood werewolf convention. There's the scene where a werewolf appears above the balcony after Christina Ricci's character taunts its fashion sense, flipping the bird and roaring "fuck you!", before dying in a hail of bullets. To be fair though, the movie turned out this way in part due to Executive Meddling.
Wonder Woman (2017): Ares looks pretty sinister, so long as he's got his helmet on. When Diana knocks it off, all audiences can see is Remus Lupin's head on Sauron's body. However, even when wearing the helmet, Ares lacks the shadowed face and red eyes of his more well-known counterparts, meaning Sir Patrick's 1910s style mustache is distractingly visible under the helmet.
The second segment of XX, The Birthday Party, revolves around a woman trying to hide the fact her husband has died during their daughter's birthday party, but it's difficult to find scary at all due to the absence of any real threats, the lack of a spooky atmosphere (outside of a handful of cheap Jump Scares) and the sheer ridiculousness of the story (the woman could resolve the issue quite easily by calling the police, but chooses to try and hide the corpse in increasingly complicated and outlandish ways). It works a lot better as a straight-up Black Comedy than as a horror story, even though it's part of a horror anthology film.