The Big O uses this coupled with the Rule of Funny for maximum impact. In Episode 18, Jason Beck decides to pwn Roger Smith with a robot that's a walking parody of the Power Rangers, Mazin Kaiser, Getter Robo, Voltes V, and Zambot 3, and the pwnage he gets for his trouble is totally and epically hysterical. After getting its own lengthy transformation sequence complete with poses and Beck shouting the robot name with background flash effects, Roger just looks at Beck with the most bored expression on earth and just shoots it to pieces. For bonus points, the player can recreate this scene in Super Robot Wars Z and get new weapons for The Big O as a reward.
Dragon Ball: During Goku's fight against Piccolo Jr., the Demon King's son hits Goku with a powerful penetrating energy attack. Unfortunately for him, Goku manages to keep standing.
Goku: "It's a good thing you aim as bad as you fight! You missed my vital organs!" Piccolo Jr.: "ALL OF THEM?!"
Dr. Gero does this multiple times during the Android Saga. For starters, whether it was actually impossible or he just didn't bother, not following Goku to Namek with his observations and combat data recording truly deserves this trope. What with the Super Saiyan transformation and all…
For someone who researched modifying humans to turned them into killer cyborgs, the fact that he concluded that Goku won't become that much stronger because of his age is a big In-UniverseCritical Research Failure.
In another bit of In-UniverseCritical Research Failure, him not realizing that the Z-Fighters can raised their powers in short busts and not taking that into account for his energy absorbing android models.
Him not knowing that Piccolo has telepathy. He must have seen at several points that Piccolo and his father, King Piccolo, had the ability to communicate with only their thoughts. He obviously didn't know this since he was shocked that Piccolo was able to call for help despite his mouth being covered.
During Vegeta's fight with Pui Pui in the Buu Saga, Babidi transforms the environment into that of Pui Pui's home planet of Zoon, which has gravity 10 times that of Earth, in order to give Pui Pui an advantage. It backfires completely, because not only does Vegeta regularly train in 450 times Earth's gravity, but his own home planet of Vegeta had gravity equal to that of Zoon anyway.
Vegeta: Maybe... if your planet had five hundred times Earth's gravity, you'd have an advantage, but ten? I don't even feel it!
When Super Buu transforms Vegito into candy, it seems all hope is lost...until it turns out that piece of candy is still able to talk, fly, and fight. Being so small and agile made Vegito so hard to fight that Buu had to actually transform him back to normal.
Animated GIFs of Osaka kicking her shoe off and inadvertently causing various epic failures has become a minor internet meme. The most famous edit of this scene has her kick the shoe up, have it fly over the horizon, and make a ship explode◊.
There's also the Jump Rope arch-fail in episode 12... Tomo getting slapped in the face by the rope while jumping? Amusing, but not an epic fail. Osaka somehow managing to trip and Face Plantwhile she's the one holding the rope? How on Earth did she do that!?
Nakamura's attempts to use the Poisoned Chalice Switcheroo to capture Nano. Not only does she end up drinking the coffee she herself drugged twice, but the second time was well after the first, which demonstrated that such drugs don't even work on the Robot Girl.
Chapter 182 features everybody except Yukko falling asleep in class during a test. Yukko nabs this opportunity to start copying answers off everyone else's worksheets. Yukko is just Genre Savvy enough to realize that copying from just one worksheet could expose her due to identical answers, so she copies a different answer from each person in class. Such is Yukko's luck that every individual answer she copies is incorrect, resulting in a score of zero.
Lampshaded in his death scene, as his having taken out Integra's eye leads him to use several of his final words crowing over finally hitting what he was shooting at, indicating his abysmal marksmanship really had been a lifelong issue.
Asuna of Mahou Sensei Negima! once tried to light her crush's cigarette, but accidentally lit his beard instead. She then doused the fire with the first liquid she could get her hands on — piping hot tea.
The Digimon Adventure movie Our War Game has a moment of this that is both funny and serious. Taichi, in a frustrated manner, bangs on the side of the monitor he's using to observe the fight between the Digidestined's Digimon and Diablomon. The computer it's connected to crashes. Hell, he didn't hit it very hard at all. Taichi's reaction (AKA, his expression) is priceless. Though, besides being funny, it serves as an Oh Crap! moment as WarGreymon is now more or less a sitting duck for Diablomon.
Kurumi's Evil Plan in Kimi ni Todoke to split up Kazehaya and Kuronuma by making Kazehaya think that Kuronuma likes someone else. Not only does the Batman Gambit end with the misunderstanding cleared up, Kazehaya becomes inspired to actually act on his crush and it makes Kuronuma aware of the fact that she likes him too, further deepening their bond. Kurumi, thinking it actually worked, ends up confessing to who she thinks is Kazehaya with her back turned...only to discover that not only has she confessed to the class' idiot gym teacher instead (who rejects her), but Kazehaya accidentally walked in on the confession. Just to rub it in, he kindly informs her that he won't tell anyone else.
Fresh Pretty Cure!: Villainous example — the job of a Labyrinth is to use monsters to cause misery so they can gather it as energy. Enter Westar. His plan involves using a living wig to change people's hairdos to cause misery. It totally backfires and instead everyone hit by the monsters attack is intensely amused. Incidentally, this scene is one of the most meticulously animated in the whole series.
The last scene in the episode reveals that Westar did manage to cause a small amount of misery to be gathered: his own.
Westar gets another one when he devises a plan of broadcasting his fight against the Precures, in hopes that everyone would see him beat the Precures and lose spirit. That backfired AGAIN when the Precures realize that it serves as more reason that they should fight harder. Cue massive asskicking while the crowd are cheering for the Cures instead of succumbing to despair.
In Yes! Pretty Cure 5, Nozomi was revealed to have been kicked out of just about every club in school prior to her becoming a Pretty Cure. One episode revealed that she was kicked out of the Drama Club after only two days. Sadly, they're all Noodle Incidents.
You have to be a particularly intense kind of stupid to use an explosive as your means of transportation in a major competitive event. In one episode of Pokémon, one person has an Electrode as his mount. One pitfall later, he's out of the race...as are several other contestants.
Another contestant uses a Rhyhorn as his mount. Rhyhorn is basically a rhinoceros made out of rock. Not the best you could use, but pretty good. He's actually doing pretty well, but then he comes to the first jump over a river and...sinks like, well, a rock.
Pikachu enters with Squirtle as his mount. The two already had a problem catching up with the other racers, but then Squirtle tried running up a slope...
In the episode "Holy Matrimony!", James tried to lie about his status, claiming that he froze in the snow and died after running away from home after faking amnesia. The other characters (even Brock, the wise person of the group) fell for it, despite James being the one telling the story. Misty was the only one who actually realized that his story was false.
In two episodes of DP, Ash, Dawn, and Brock (especially Brock) were fooled by Jessie, James, and Meowth's disguises. Normally, it isn't noteworthy, but in this particular case, they were still fooled even when Jessie, James, and Meowth's disguises...just consisted of glasses and green coats. It didn't even cover up the telltale red R on their uniforms properly, and there was a light in the background shining on them. It's not even the worst offender either: an entire populace, and Brock, participated in a contest about which Croagunk was the best looking. They chose Meowth, despite his disguise actually being so bad it would have been impossible to mistake him for a Croagunk.
"The Problem With Paras" has a Paras so weak that even the tiniest attack makes it faint. Especially notable is Squirtle shooting a tiny trickle of water at it, since Paras is half grass-type and grass resists water.
It's hard to tell what's worse in the above example, the Paras for being so weak it fell to a deliberately softened attack it was already resistant to, or Ash for deciding, after the above takes place, to send in Charmeleon of all things, believing it'll have better luck in throwing a match against the thing. Ash cannot control Charmeleon. He can tell it to lose a match, but Charmeleon won't listen, and fire is four times super-effective against Paras.
Most of what Cameron does. Such examples include: thinking the Unova League in Unova was going to be in Ecruteak City in Johto; thinking he only needed 7 badges to enter the League; somehow forgetting one of his Pokemon on the sidelines before a gym battle; pitting up Pokemon with a 4x weakness against a Pokemon with the exact 4x type advantage (Twice in one battle, too); and bringing only 5 Pokemon to a 6-on-6 battle.
Jessie in her first ever Pokemon contest. She uses Seviper and in the appeals round starts off by telling Seviper to use Sacred Fire (a move only legendary Ho-Oh knows) and then goes through a book listing off moves that Seviper doesn't know including Double Kick. She then does use a move that Seviper knows, Poison Tail, which is then only used on her and sends her flying. The judges give her a score of zero.
Sullivan from the episode "Whiscash and Ash" has been trying for years to catch a particular Whiscash, and has failed utterly. He even fails to capture it when using a Master Ball, a Pokeball that never fails and is guaranteed to catch a Pokemon. Failing to catch a Pokemon even with a Master Ball is a whole new level of failure.
In the Arrancar Saga of Bleach, Dordoni manages one during his introduction. While giving a speech and running, he falls off the platform he was running on when it ends and crashes into the ground. And this guy can walk on air.
Also, in Chapter 470 Rukia tries to use Kido while stuck as a plushie, and fails spectacularly.
Bobobo-bo Bo-bobo are often filled with these moments, especially in fights, whenever some attacks go wrong or just don't work at all.
Given the sheer craziness of the show, sometimes these epic fails would become weaponized in and of itself.
Don Patch can inject enemies with his "Idiot Serum", which forces them to epically fail in various ways. Beauty finds this absolutely terrifying.
In the first episode of Cube×Cursed×Curious, Fear tries her hand at cleaning. Granted, she's never done anything like that before, but that's no excuse for trashing the whole house. Some of the things she did just went against common sense.
Naruto tries to reenter Biju Mode in an attempt to stop Obito prematurely. His chakra flares up, his Badass Longcoat forms...and then everything sputters out. The look on his face, Sasuke's, and Tobirama's says it all.
Tobirama: Are you trying to make our situation even worse? You're as goofy as your father, so much so that even he'snote One of Naruto's father's students dumbfounded.
Another example is episode 3, when Nagato and Achakura first met when Achakura was restored to her normal self... well, not back to her normal self, because Achakura was in chibi form. During one scene, Achakura complains that she did not want to sit in the chair, and so Achakura was placed on a pillow, and then, when Nagato walked out of the room, Achakura was flung into a wall, and when Nagato came back, Achakura was sitting on a chair with a side dose of a Cranial Eruption, and then when Nagato asked that Achakura finally decided to sit in a chair, Achakura said that she did not want to hear about it.
Later on, one episode, when Nagato's friends left, Achakura, who was attached to a spring, comes out of a jack in the box, and Nagato puts the lid back on, which makes Achakura 100% mad! Then, when Achakura yells at Nagato, she went so high that Achakura hit her head on the ceiling VERY HARD. Which resulted in a Cranial Eruption (remaining for the last few moments of the episode) for Achakura.
The Daily Lives of High School Boys skit High School Boys and the Way We Are is basically one string of failure after failure in the Literature Girl's trying to invoke romantic situations with Hidenori, ending with her breaking down crying (and accidentally knocked out cold by Hidenori).
Slayers: Sylphiel, being a specialist in white magic, lacks the focus and killing intent to cast black magic at first. Her initial attempts to cast Flare Arrow ends up more like a Flare Carrot.
In a filler episode of Beelzebub, the students of Ishiyama High had to take an assessment test. One guy cheated on filling in his name.
Gintama is filled with these moments involving the Yorozuya but every encounter with the Shogun will involve epic failure in outstanding ways.
Made it more hilarious if the music theme is 'Shogun ka yo' and Gintoki (and Shinpachi) screams 'SHOGUN KA YO!!!!'
In Soul Eater, Soul and Black Star try to fight Death the Kid... and make total fools out of themselves. The funniest point is when Soul turns into his scythe form for Black Star to wield, and Black Star fails to catch him and the blade goes into his head.
Then it turns into an epic fail for Kid when he passes out with them...after noticing they cut off part of his hair, making it asymmetrical.
In an early (the second) episode of Yu-Gi-Oh! 5D's, Uryu uses a Continuous Spell called Retribution of the Ant Lion against Yusei, which causes 800 damage to a player if one of his monsters is destroyed. Clearly he didn't read the card's effect clearly, because he's a little surprised when he intentionally destroys his own Pinch Hopper to use its effect, and then takes damage from it himself. (And ultimately, the card causes him to lose the duel when Yusei destroys three of his monsters at once.
In My Bride Is a Mermaid, when Kai is Mistaken for Dying, he gives a Last Request to have a final duel with his love rival Nagasumi. Even though Kai is a trained swordsman, his panic over how he's supposedly dying makes him flail his sword around ineffectually, allowing Nagasumi to easily beat him down with his fists.
In episode 23 of Happiness Charge Pretty Cure, Megumi and Yuuko arrive in their Cure forms to the scene of a battle, do their introduction phrases and poses... only to find out they were too late - Hime and Iona had already beaten the Monster of the Week by themselves.
Cocoa attempts to hit the shuttlecock in episode 5 when Chino serves it to her. She tries to act cool and confident, only to then miss it when she swings.
Chino attempts to use a badminton move Rize taught her in episode 5. It looks cool and she has a Battle Aura as well, but then she hits the shuttlecock into the net, getting it stuck, and also passes out from using up too much energy.
Cocoa attempts to flip a pancake in the air in episode 7. But she flings it a bit too high, and it lands on Chino's face. And later in the episode, she misspells "Rabbit House" on a flyer as "Rabbit Horse".
Wakamatsu from Monthly Girls' Nozaki-kun is so strung out by Seo's roughhousing during basketball games that he decides to tell her off on the school roof...taking cues from shoujo manga. He screws up so badly in expressing his disgust for her that the whole thing looks like a love confession.
Doraemon has Nobita Nobi, an utter poor student who gets straight zeros in every exam unless he's aided by Doraemon's gadgets. Apparently he has bundles of the sheets at home.
The first time Sailor Chibi-Moon attempted to use her Pink Sugar Heart Attack. After shouting the attack's name nothing happens. After a few seconds her wand starts flashing and shots out tiny hearts... that travel about a foot in front of her and fall to the ground. The Monster of the Week gets so bored she begins drinking tea. Of course, that distraction allows Chibi-Moon to slowly creep forward so her attack hits, but even then it's more of an annoyance than damaging.
The second time Ryuko tries to use Senketsu, he won't transform, because she didn't realize he needed her blood. She has to run away from the tennis club.
During the tennis match, Ryuko's racket explodes on contact with the ball, failing to even slow it down.
Gamagoori's evasive driving involves a spin. It ends up about as you'd expect.
Gamagoori: We're out of control! Ryuko: NO SHIT WE'RE OUT OF CONTROL! THAT'S WHAT HAPPENS WHEN YOU CRANK THE WHEEL LIKE THAT YOU ASS!!
Puella Magi Madoka Magica the Movie: Rebellion: Madoka being taken off-guard by Homura at the end. For reference, Madoka is The Omniscient, and even if one thinks that she didn't have her all-seeing abilities because of Kyubey's machinations, she still had quite a while to view, quote, "Everything that ever happened and everything that ever will", unquote before the events of the movie. Whatever the case, this particular blunder costs her her powers and memories, elevates Homura to demonhood and twists all of reality into knots.