The Gods Must Be Crazy is a collection of epic fails every ten minutes of the movie. Ay ay ay ay ay. What's worse, roughly half the wacky predicaments ensue simply because at the beginning of the movie, someone throws an empty Coca-Cola bottle from an airplane. Seriously. We never even learn the litterbug's name.
In the Garfield movie, there's a scene near the middle of the film where Garfield is upset over Odie. He proceeds to vent this frustration by smacking Odie's favorite ball. The ball knocks an object over, then that object knocks something else over, and this chain reaction continues until the entire wall-high shelf tips over and onto Garfield. When Jon comes back inside, he is not happy. Garfield lives, of course.
It also gives us footage of various foreign countries' hilariously botched attempts to replicate the Iron Man armor. Turns out that without an actual set of the armor to reverse-engineer, trying to do this absolutely requires a Stark-level genius. Not too many of those around.
The Mk. 42 in Iron Man 3 falls apart at the slightest jolt. Of course, it's designed to be able to come apart and fly towards Tony and assemble around him, but it falls apart too well. An epic scene where Tony is facing off against the Big Bad, JARVIS informs him that Mk. 42 is on the way. Heroic music plays, as Tony uses a gesture to get the armor to assemble on him... and the armor trips and falls apart.
Tony Stark: (eyeroll) Whatever.
In the Fantastic Four movies, Ben mentions that Johnny "washed out of NASA for sneaking two Victoria's Secret wannabes into a flight simulator. They crashed it into a wall. A flight simulator."
Mulholland Drive has a scene where a hired killer kills his victim and then tries to fake suicide by putting his gun into the victim's hand. While trying to do so, he accidentally pulls the trigger and the bullet goes through the (fairly thin) wall into the neighboring flat, hitting a fat, ugly woman. He then goes into said flat and attacks the woman, who turns out to be stronger than he expected. He eventually overpowers her and tries to drag her into the flat where he killed the first guy in order to fake a suicide-with-murder scenario. While passing the floor, he is observed by a janitor who apparently doesn't speak English, but slowly follows him into the flat. Back there, the killer first kills the woman, then the janitor enters the room with his vacuum cleaner. He also shoots the janitor, but by accident, the vacuum cleaner is turned back on again. He then pulls the janitor into the room. Finally, he tries to turn off the vacuum cleaner... by shooting at it. The vacuum cleaner catches fire, which sets off the fire alarm.
In Snatch... pretty much anythingSol and Vinnie put their minds to. In their defining moment, they were hired to take a briefcase from a man who had been sent to place a bet at a bookie's. They are to rob the bookie's place as well, so it doesn't look too suspicious to the guy with the briefcase when they steal the case from him. In the end, they'll get the cash from the bookie's, their employer gets the case. Unfortunately, their getaway driver, Tyrone, Drives Like Crazy and backed into the van their victim had used to get to the scene, knocking him out and trapping him inside it. Later that night, they see someone carrying a case go inside, and without attempting to verify the target, they enter the bookie's, only to find that it's (obviously) the wrong person, and furthermore that the bookie's has no cash because all bets are off. Then the cashier lady turns out to be a Badass Bystander who deftly disarms Sol of his shotgun and trips the alarm. Then they attempt (and fail) to open the front door. Reasoning that it's a security door that locked when the alarm was pushed, they try to Shoot Out the Lock. The door turns out to be bulletproof, and Vince gets his leg grazed by the ricochet. They fall down in exhaustion and take off their ski masks, at which point they notice the security camera that's just caught them both unmasked. And then, to top it off, Tyrone shows up to get them... it turns out the reason they couldn't open the front door is because they tried to push the 'pull' side of the door. The pincher is that the pair are completely unknown in that part of the underworld, and the camera fails to be of any use because the owner doesn't recognize them... but Tyrone is recognized. Epic Fail indeed.
Pretty much every single plan Jason conceives in Mystery Team. Most notable is when a speech on how a certain character won't shoot them gets him shot.
In the 2008 Get Smart movie, Maxwell Smart is given a tiny grappling hook launcher, and while using it to free himself, manages to hit everything except what he was aiming for, including a secret button that drops him out of an airliner. In flight.
Made slightly more epic by the fact that the grappling hook launcher was part of a Swiss Army Knife. You know, the thing with a blade on it! For cutting!
Monty Python and the Holy Grail: The knights are crossing the bridge of death and must answer the bridge keeper's three questions, and if they fail any one, they will automatically fall off the bridge to their death. The first two questions always ask one's name and quest, but the third is always random, ranging from something impossibly easy like "what is your favorite color" to a ni-difficult "what is the capital of Assyria." Galahad lucks out and manages to get the "favorite color" question... and still manages to screw up his answer, leading to him plummeting to his death. About as justified as this trope can get, since he was just fluidly and unthinkingly repeating the previous knight's answers to the same questions and didn't realise that wouldn't work for favorite color until it was too late.
From Pulp Fiction, one of the guys at the apartment where Jules and Vincent go to retrieve Marsellus Wallace's briefcase ambushes them and shoots at the duo at very close range... and misses every shot. All three pause to stare in surprise.
To elaborate: Two detectives are chasing some jewelry thieves to the roof of a 20-story building, and the thieves escape by zipline (which they, of course, cut after using). The detectives decide the best course of action would be to jump off the roof and land on the bushes...despite the fact that the pavement underneath doesn't even have bushes, or anything that can be used to safely land on. Three guesses what happens next, and the first two don't count.
In Repossessed, Ernest and Fanny Weller, two corrupt televangelists (parodies of Jim and Tammy Faye Bakker), decide to televise a real exorcism and take phone donations. All is going well until Fanny demands a chance to sing on television. The money donated swiftly starts to go down.
The entire US military does this in Godzilla (1998). First, they miss the skyscraper-sized dinosaur with rockets and heat-seeking missiles from close range and destroy more of the city than the lizard does. Somehow, the monster was able to hide in a city of eight million.
The Navy trying to attack Godzilla just as he rises outside of San Francisco Bay in Godzilla (2014). One of the ship rockets hit a supporting cable, prompting a soldier to tell them to stop firing due to civilians on the Golden Gate Bridge. They still keep firing at him, and a hole gets torn in the bridge in the chaos.
In Star Trek III: The Search for Spock, Kirk and his True Companions steal the Enterprise. The shiny new Excelsior, in hot pursuit, powers up its revolutionary transwarp drive... which promptly conks out due to Scotty sabotaging it beforehand, complete with sputtering engine noises, leaving Starfleet's "Great Experiment" adrift and having to be towed back to Spacedock.
The Lord of the Rings: The Two Towers: When the Ents (gigantic living trees) hold a council, they demonstrate just how mind-bogglingly slow they are at doing anything.
Treebeard: We just finished saying... "Good morning."
The 1989 film: Batman programs the computer in his Batwing to fire two machine guns and several missiles at The Joker. Every missile and bullet completely misses. Even more humiliating when the Joker causes the Batwing to crash to the street below with a single shot from his (admittedly very long) gun.
Batman Returns: The Penguin snatches up an instrument panel from the wreckage of the Batboat and tries to use it against Batman, assuming it's some kind of weapon. It turns out to actually be the device that overrides the frequency jam on the Penguin's radio signal to his pet penguins to launch their missiles at Gotham City, and as a result the penguins fire their missiles at Penguin's own hideout, completely destroying it.
After Erik has just stopped a missile strike from the US Navy, Xavier tries to get Erik to call off his counterattack by saying that "they were Just Following Orders!" He said that to a Holocaust survivor. Magneto's face and quiet voice show everyone just how utterly Xavier has failed to convince him, before he returns the missiles to sender.
In The Man with the Golden Gun, Hip and his nieces rescue James Bond from Hai Fat's dojo. The plan goes well, until Hip drives off without Bond, despite his nieces trying to tell him that the man they were sent to rescue has been left behind.
Toy Story 2: "Prepare to meet, Mr. Angry Eyes!" quoth Mr. Potato Head as he rushes to the attack in Al's apartment. After switching his regular eyes... for an extra pair of shoes. So naturally he just runs into the furniture and looks like an idiot. Jessie's WTF facial expression makes it even better.
In The Men Who Stare at Goats, Lyn crashes into a rock in the middle of the desert, the only such object for miles around. It was probably destiny.
Trying to break Simba and Nala up, Timon from The Lion King 1 ½ throws a beehive at them... only for the hive to go ahead and the bees to stay right above his head. Why this happened... the world may never know.
From Captain America: The First Avenger, S.H.I.E.L.D's major Critical Research Failure when Steve Rogers has been thawed in a fake 1940's hospital room. Everything else in there was fine (a woman even entering in a suitable getup) - except for the radio broadcasting a "live" baseball game, from 1941. Rogers was frozen in 1945, and he was AT that game. They didn't even bother to check whether the game was from after he went MIA.
In Captain America: The Winter Soldier, this trope is used to surprisingly serious effect. After WWII, SHIELD recruited a number of HYDRA scientists to do science and engineering for them. This in and of itself isn't a bad idea; it happened in real life, with the U.S. recruiting Nazi scientists like Wernher von Braun to work on their space program. The difference is, von Braun and his cohorts had mainly been Punch Clock Villains, cooperating with the Nazis out of fear and duress. But HYDRA was staffed by dyed-in-the-wool supervillains. Fast-forward to the present and Armin Zola has essentially converted SHIELD into a massive HYDRA operation working under deep cover. It's so bad that the heroes have to literally destroy SHIELD to save the world.
In Tangled, Rapunzel has a montage of epic fails trying to get Flynn Rider into a closet. It should be noted that he was unconscious, and it only ends when Rapunzel decides having the doors closed with his fingers poking out is close enough.
Harry: I mean, basically, if you're robbing a man and you're only carrying blanks and you allow your gun to be taken off you and you allow yourself to be shot in the eye with a blank which I assume that the person has to get quite close to you then, yeah really it's all your fault for being such a poof, so why don't you stop wingeing and cheer the fuck up.
Done deliberately in Aliens, as a way to emphasize how drastically unprepared the Colonial Marines are against the xenomorphs. The unit is sent into a highly critical part of the Hadley's Hope colony (the atmosphere processor), after reviewing its schematics. They are knee-deep in the xenomorph hive when Ripley points out to them that the machinery can be pierced by conventional weaponry, which leads a frantic and inexperienced Gorman to tell the Marines to give up all their ammunition (except for flamethrowers) to one man, without explaining why. When the xenomorphs inevitably crawl out of the walls, said soldier is the first casualty, causing everything to descend into anarchy. Apone stands in one spot trying to hear Gorman's orders just before he's abducted by a xeno, the only soldiers who survive are the ones who kept spare magazines and/or backup weapons, Drake and Vasquez stage a tactical retreat by shooting wildly with smartguns (which causes the damage that would eventually overload and destroy the colony), and Gorman is knocked out by unsecured cargo in the APC during the escape.
In Gangster Squad, the squad's first operation as a unit devolves into equal parts slapstick and failure. They try to take down one of mobster Mickey Cohen's casinos by storming it at gunpoint, only to be met by a group of armed officers who assume they're robbers and try to arrest the group. On the squad's escape out of the casino, their car breaks down, and David and O'Mara get arrested after giving the car a running boost. The two men get beaten, arrested, and sent to jail, where Cohen sends men intending to pick them up and execute them. The squad arrives to save the two men, but Kennard's plan of tying a rope from his vehicle to the prison window bars fails (the bumper gets ripped off the car), Keeler's plan to cut the power results in chaos in the prison block, and the whole thing would have gone south if Wooters hadn't show up.