Alice has asked Bob to help her learn about a certain thing (for example, how to drive, since she's never bothered to learn). Or, maybe Bob has been assigned to act as a mentor of sorts at the workplace since Alice is new there. However, rather than teach her properly, Bob decides to teach her all the wrong things. (This trope assumes that Bob is doing it on purpose; cases where Bob is making a sincere but incompetent effort don't count.)
The reasons for this vary. Perhaps Bob doesn't want Alice to pass her driving test; maybe he's afraid Alice will outshine him at work, so he tries to get her fired; perhaps Bob's having fun at her expense; or maybe Bob's just an asshole. Or Alice is a Deceptive Disciple and Bob realizes this. Whatever happens, you can be sure hilarity will ensue.
Invariably, in comedic shows Rule of Funny dictates the sabotutor suffers from Laser-Guided Karma, most commonly being that their attempts to sabotage what they taught wind up impressing the ones calling the shots, netting them praise. Alternatively, if the sabotage was to steal a role and the sabotutor succeeds, it'll turn out they just saved their unaware charge from an absolutely hellish experience.
This doesn't have to just be a tutor in the academic sense, but any time somebody is instructing another person in a subject. If it fails, may lead to Springtime for Hitler.
- In A Certain Magical Index, whenever the British character Laura Stuart tries speaking Japanese, someone will invariably tell her she's saying things wrong. Apparently, the reason is that Motoharu Tsuchimikado was the one who taught her the language, and he purposefully taught her incorrectly as a joke.
- Dragon Ball: After hearing Goku got stronger by climbing Karin's Tower and drinking the sacred water, Taopaipai tries to do the same, but Karin can immediately tell he's a bad guy. He pretends to help by giving the water right away, but this actually defeats the purpose—it's just regular water, while Goku's improvement was from climbing the tower (twice!) and getting fast enough to catch Karin. Karin even gives Taopaipai a cloud to ride back to the ground on so he won't get anything from a climb down (and has it drop him just high enough off the ground to insult him).
- When Amelia asks Lina to teach her the Dragon Slave in a season one episode of Slayers, Lina deliberately puts her through a pointless Training from Hell that has absolutely nothing to do with magic in the hopes that Amelia will give up and go away.
- In Welcome to the NHK, Misaki's stated goal for Sato is to help him overcome his hikikomori tendencies and become a functional member of society. In truth, she wants to make Sato dependent on her, so as to assuage her own feelings of worthlessness.
- In an Archie Comics story, Reggie mocks Jughead, in front of the class, for getting all his history facts mixed up. Miss Grundy punishes Reggie by assigning him to tutor Jughead. The resentful Reggie deliberately teaches him even more mixed-up history. This ends up working too well as Reggie, bragging about this to his friends, finds that he himself has gotten all his history knowledge mixed up. When his friends try correcting him, they find it's happened to them too. Before long the entire history class is so confused that everyone flunks the next test. (Reggie himself takes twenty minutes to "remember" his name is Betty.) Miss Grundy and Mr. Weatherbee, reviewing the results, decide the only solution is to go back to the very dawn of history and start teaching from scratch.
Weatherbee: Start right off with Amos and Andy in the Garden of Eden!
- Calvin and Hobbes: Calvin's father sometimes teaches Calvin untrue things on purpose, like telling him colour came to the world around 1950 and before that the world was black and white. Bill Watterson claims his own dad did the exact same thing.
- In one Dilbert strip, the Pointy-Haired-Boss reviews a trainee's work performance and concludes that his trainer has been playing a six-month-long practical joke on him. For some strange reason, the trainee doesn't find it funny.
Trainer: Sometimes there's a fine line between criminally abusive behavior and fun.
- A Running Gag on FoxTrot whenever Jason does anything related to tutoring. One of the few times he didn't do this was when Paige decided to pay Jason in function of her grade.
- Peanuts - After Linus was born, and he was still younger than the other characters, Lucy decided to take him under her wing and teach him Little Known Facts. Lucy may just have been a Know-Nothing Know-It-All, though.
Lucy: This is an elm tree. Someday it will grow into a mighty oak. You can tell how old it is by counting the leaves.
- At least two times in Tank Mc Namara, a veteran football player is instructing a novice who's expected to replace him ... and advises the youngster to make a racist remark. "All the black defensive linemen think it's a barrel of laffs."
- Guru of Dragon Ball Z Abridged encourages Nail to stand up to Freeza by telling him that he's a champion of the old ways. After he leaves, Guru comments that if he'd taught him in the new ways, he might have stood a chance.
- This is a common plot device used in Naruto fanfiction. Naruto's lack of skills is often attributed to his teachers deliberately sabotaging his ninja training. This provides a convenient way for authors to explain his rapid growth in power once he begins learning things correctly.
- In the First Try Series, Naruto and many other Academy students were sabotaged by Academy teachers as part of a large-scale plan to weaken Konoha.
- In Naruto: The Game of Life, Mizuki specifically sabotages Naruto, while certain rich businessmen pressure the teachers to dumb down their curriculum for everyone so their own kids can pass.
- Dogtooth: The father and mother of the main characters purposefully teach them incorrect definitions to words in order to manipulate their worldview and prevent them from ever learning certain concepts.
- The Karate Kid Part III: When Mr. Miyagi refuses to help train Daniel for the upcoming karate tournament, Terry Silver offers to train him. Since Silver is actually working with Daniel and Miyagi's enemy John Kreese, he teaches Daniel to give in to his anger and aggression instead of useful skills. Daniel, who was really frustrated by Miyagi's rejection, falls for it and eventually injures his hands when he loses his temper punching a wooden dummy. Silver mocks him for falling for it, then he, Kreese, and their goons start beating him up before Miyagi rescues him.
- The above-mentioned Wimp Lo from Kung Pow! Enter the Fist is a result of this. Most likely because he was an arrogant fool that wanted to be the Chosen One, the mentors purposefully trained him wrong as a joke.
Wimp Lo: "I am bleeding! Making ME the victor!"
- This was apparently an actual practice for certain schools.
- Twice in My Big Fat Greek Wedding. Ian asks Toula's brother Nick how to say thank you in Greek and Nick teaches him to say "Nice tits" instead. Later, Nick offers to teach Ian how to call everyone inside for dinner in Greek, but Ian has wised up slightly and asks for a second opinion. Unfortunately, the person he asks is Nick's cousin Angelo, who is in on the prank and confirms what Nick said, causing Ian to announce "I have three testicles!" to the entire Portokalos clan.
- Darth Sidious in Star Wars: Episode III — Revenge of the Sith, and by extension the Sith in general. The Rule of Two states that the Sith can only exist in pairs of two, a master and an apprentice to eventually supplant them. However, while it sounds good on paper due to the Chronic Backstabbing Disorder encouraged by the Sith Religion of Evil (as groups of inexperienced apprentices ganging up on their master would weaken them as a whole), very few Sith actually followed it the way it was intended. Apprentices would kill their masters before they actually surpassed them and the masters fearing this would intentionally sabotage their training by withholding some of what they know as a trump card, with the intent of just keeping apprentices around to do their dirty work for them. It's implied Sidious lied and never actually learned the powers he promised Anakin, and planned to do away with the Rule entirely to replace it with his self-styled Rule of One and live forever with Vader as his cyborg slave.
- In Captain Corelli's Mandolin, Corelli wants to get on with the people whose village his men are occupying, so he asks an Italian-speaking local to teach him how to greet the villagers in their own language. The "greeting" he gets taught is thoroughly impolite and causes him to become even less popular.
- The Deptford Mice book The Alchemist's Cat features a stuck-up nobleman who constantly dismisses the eponymous alchemist, Elias Spittle, then makes the mistake of demanding Spittle provide him with a list of French phrases to greet some guests at court. Spittle, naturally, takes full advantage of this, resulting in the nobleman losing his title when he utters a string of insults to the French guests, ending in him telling the king to sew a button on his coat.
- Doc Savage: The rivalry between Ham Brooks and Monk Mayfair goes back to World War One when a practical joke landed Monk in a military jail. Ham had taught Monk some insulting French words, presenting them as compliments. Monk used them while speaking to a French general and got locked in the guardhouse.
- There's a whole series of humour books called Great Lies to Tell Small Kids.
- Subverted in Harry Potter. Harry suspects Snape of this when Snape teaches him Occlumency. Turns out Harry's legitimately bad at it. Not that it makes Snape any less of a lousy teacher. The same applies to Potions, as Harry notes in the Half-Blood Prince that he finds Potions easier when Snape isn't shadowing over them like a bat, ready to bite their heads off over all small mistakes while he's insulting them. Turns out that while Snape is absolutely brilliant at both Occlumency and Potions, his personality makes him really bad at teaching them to other people. Especially to people who he personally dislikes, like Harry.
- Heralds of Valdemar: Both Hulda and Mornelithe act as a variant of this to Ancar. What magic they teach him is correct, but they're deliberately not training him to his full potential (and not telling him that his "full potential" is not Adept-level) in order to maintain their own positions.
- A variation in Realm of the Elderlings. Chade instructs FitzChivalry to help Kettricken become a more savvy member of court. When it comes to a popular card game, he tells Fitz to teach her to cheat, but present it as the legitimate way to play. A subversion, as the idea was that she'd become such an accomplished cheat via sleight of hand and misdirection that it would be to her advantage.
- The Holy Writ is the holy book of Safehold's Church of God Awaiting. The Church was deliberately crafted to preserve humanity while simultaneously keeping it locked in Medieval Stasis. As such, the Writ accurately describes a wide range of phenomena, but does so in a way that actively discourages questioning why and how these things happen, instead attributing them to the miracles or wrath of the Archangels. It explains, for example, the importance of sanitation, but the sicknesses that result from unsanitary conditions are the wrath of the Archangel Pasquale. The Writ uses English system measurements (inches, pounds, etc) instead of the more precise metric (meters, grams, etc) and even encourages the use of Roman numerals (I, II, III, IV) until Merlin Athrawes introduces Arabic numerals (1, 2, 3, 4) and revolutionizes Safeholdian mathematics. All of this is done in the name of keeping humanity from getting too inquisitive. It works for close to a millennium, but it was already starting to fray by the time Merlin awakens at the start of the story to destroy the Church's hold completely.
- Star Wars Legends: In the first book of the Darth Bane series, the Brotherhood's lightsaber instructor always warned his students that Dual Wielding lightsabers is Awesome, but Impractical. When Bane duels him later in the book, the instructor suddenly reveals that his double-bladed lightsaber splits into two regular lightsabers, and dual-wields them to great effect. Bane realizes the real reason for the instructor's "warnings".
- In Warrior Cats, Lionblaze claims that Ashfur (who has a grudge against Lionblaze's parents, as he was part of a Love Triangle involving them) has been teaching him to do everything the wrong way. Brambleclaw (Lionblaze's father), is shocked at the accusation because he knows it could possibly be true, but he also scolds Lionblaze for blaming others.
- In The Witcher short story "The Last Wish", Geralt recites what he was taught was a multipurpose exorcism; it turns out to be a translation of "go and fuck yourself". The Literal Genie he used it on is very angry.
- In 30 Rock, it's revealed that Drew was taught absolutely everything that way. He was just too handsome for anyone to ever tell him when he was doing it wrong. As a result, he believes you can cook salmon in Gatorade.
- In The Big Bang Theory, when Stuart is briefly dating Penny, he goes to Leonard for romantic advice. Leonard deliberately feeds him wrong or misleading advice as he has a vested interest in breaking them up. Stuart later tells Leonard that Penny was pleased with his behavior.
- In one episode of Everybody Loves Raymond, Debra asks Marie to teach her how to make meatballs. Marie, fearing that losing her domestic edge on Debra will mean no one wants anything to do with her, switches the labels on the ingredients around substituting tarragon, a strongly bitter flavoured herb, for the recipe-appropriate basil.
- Extr@ always features Nic, a native speaker of the language the series is in, teaching Sam, an American with little knowledge of the foreign language, all the wrong words, e.g. teaching "basket" as "oven" so that Sam will shock everyone by saying "the dog is in the oven". Nic does this to make Sam seem stupid and prevent Sasha (who Nic has a crush on) from liking him.
- On Family Matters, Steve Urkel once considered sabotaging someone in this way, because he saw the guy as a rival for Laura's affections. His better angels convinced him not to do it though.
- Frasier advises Marco, one of his callers to his radio show, to break things off with his girlfriend if he is not happy. The girlfriend, Catherine, comes to the studio to yell at Frasier but after finding out Marco is a commitment-phobe, Frasier and Catherine start dating. When Marco calls again for advice to get Catherine back, Frasier, against his ethics, tells Marco it is a bad idea.
- Frasier asks Noel Shempsky to translate a speech he wants to give his son at his Bar Mitzvah into Hebrew, but having failed to complete the favor Noel asks in return (getting Scott Bakula’s autograph at a convention), Noel translates it into Klingon instead. Hilarity ensues.
- Friends: Joey once taught a soap-opera acting class. One student asked Joey to coach him and prepare him for an audition for the role of a boxer, a role which Joey wanted as well. Joey advised him to play the role "homosexually". It backfired, though, because it turned out that they loved it and the student got the role.
- In Grounded for Life, Sean deliberately "torpedoes" Lily when teaching her how to drive.
- On iCarly, Carly and Sam are dealing with the problem of tutoring a bratty kid. They teach him incorrect mathematics using nonexistent numbers, and he believes them and fails his class.
- In one episode of I Love Lucy, Lucy and Ethel wanted Fred and Ricky to teach them how to play golf so they could spend more time together as couples. The boys, not wanting their wives to intrude on their one activity away from home, teach the girls ridiculously made up and complicated golf rules in hopes of making them hate the game and leave them alone. When the girls find out, they get the last laugh by convincing a professional golfer to play with Fred and Ricky using the made-up rules, tricking the boys into thinking they'd been playing the game wrong this whole time.
- On Married... with Children, Bud does this to Kelly, mainly just 'cause it's funny. Case in point: In one episode, Bud tricks Kelly (twice) into letting him help her with book reports for books she didn't bother to read. The first time, she reports on Robinson Crusoe while explaining the plot to Gilligan's Island. When Bud offers to help her a second time, he feeds her The Addams Family plot details for her report on the works of Edgar Allan Poe.
- An indirect version of this occurs in the "Dirty Hungarian Phrasebook" sketch in Monty Python's Flying Circus. Someone deliberately publishes a book with wildly inappropriate English translations of Hungarian phrases (and vice-versa) to get the user in trouble. It's the trope namer for My Hovercraft Is Full of Eels.
- Quantum Leap: In "The Americanization of Machiko", Sam takes the place of a young Navy veteran who comes back home married to Machiko, a beautiful Japanese girl, disappointing Lenore, his callous mother, and his ex-girlfriend Naomi. Having heard that Machiko is learning American customs, Naomi tells her to call the Mayor and his wife "fat" during a picnic. The poor girl realizes she was deceived when she notices they were offended, but that's the excuse Lenore needed to kick her out... fortunately, Sam goes after Machiko, while Lenore's husband gives her a short, but well-deserved "The Reason You Suck" Speech.
- In one episode, Dr. Cox has a German patient and (insultingly) asks Elliot to teach him to say, "You have fluid in your lungs" in German. Instead, she teaches him to say, "Your wife has nice cans."
- At Turk and Carla's wedding rehearsal, Carla's brother Marco gives The Todd a pickup line to use on their Spanish-speaking relatives: "I have genital herpes... for you!"
The Todd: ¡Mucho herpes! ¡Grande!
- That '70s Show: Fez and Kelso were often given deliberately terrible advice by their friends to screw with them.
- In Wings, Antonio falls for his cousin's wife, after she confides that her husband has basically turned into a leather-clad, tasteless loudmouth. When the cousin comes to him for relationship advice, Antonio's first move is advising him to double down on his new personality (though he later thinks better of it).
Antonio: Have you tried wearing more leather?
Dominic: [looking at his outfit] Where?!
Antonio: I don't know. Hats? Gloves?
- In Teenagers from Outer Space, human characters have the ability "Fake Out", representing their ability to convince an alien visitor of almost anything regarding Earth culture, customs, and what is cool, since after all, a human would be an expert on the subject. (The attempt succeeds on a d6 roll of three or higher.) Teaching them wildly inappropriate things is the most common practice. (Although telling the hot alien babe you want to date that kissing is a standard form of casual greeting will backfire horribly because she'll greet everyone that way.)
- Played as a dramatic plot twist in Jade Empire. It is revealed that your master deliberately built in weaknesses into your fighting style, so that he could take you down after revealing that his name, Sun Li The Glorious Strategist was well-earned. The weakness is mentioned repeatedly by various masters, one even suggesting that your technique seems as if it tricks opponents into seeing an opening that isn't there. It was specifically designed by Sun Li in such a way that only he can take advantage of it and no one else.
- From the Street Fighter mythos: While training Dan Hibiki, Gouken asks him his reason for taking up martial arts. When Dan tells him that it is so he can kill Sagat to avenge his father's death, Gouken lied and told him that his training is complete. Dan believes that there is nothing left for him to learn when in fact he is very lacking in technique. It also led to The Blind Leading the Blind as Dan created his own dojo with one unfortunate person actually learning his incomplete moves. The poor soul who took up Dan's classes? Chairperson.
- Dominic Deegan: The title character's father, Donovan Deegan, is an accomplished bard who thinks he's in good standing with the orc tribes, who have taught him their language. The orcs do like him a lot, actually, but they've taught him complete nonsense as a joke. ("My landmass erupts with kittens.") Also, the heroic title he's been given that he bears with pride literally translates to "Little pink man who wears pink." Then it turns out he actually speaks fluent, genuine orcish and was aware of the whole joke from the very beginning. He only played along because it was funny. Again, he's a bard.
- Professor Steve pulls this off in the Professor Brothers short The Substitute.
- Skippy's List: 123: I should not teach other soldiers to say offensive and crude things in Albanian, under the guise of teaching them how to say potentially useful phrases.
- The Zompist phrasebook is mostly correct, except for some translations that are fake. Especially, but not limited to, the directions.
- In early outlines for Avatar: The Last Airbender, Iroh was an Evil Uncle who deliberately taught Zuko firebending poorly, under orders from Fire Lord Ozai. In the actual show, Iroh is a Cool Uncle unquestionably loyal to Zuko, and a very reliable mentor.
- Discussed in one of the most memorable scenes of Ben 10:
Gwen: You trust me to help kick alien butt — why won't you trust me to teach you how to dance?
Ben: 'Cause you're probably just gonna trick me into looking like some dancing doofus.
Gwen: You don't need my help to dance like a doofus. So get over yourself! And give me your hands...
- In The Cleveland Show episode "Brotherly Love", Rallo gives Cleveland Jr. dating advice. After Rallo falls for the girl, his advice includes being on the phone all the time because it makes you look important and try to solve a problem immediately without hearing all the details. He also says that if she has anything to say, take a long exhale, roll your eyes, and say "what".
- On King of the Hill, Peggy pulls this on Lucky when he asks her to help him get his GED so he can propose to Luanne. She's hoping they'll break up instead. She succeeds, but unfortunately this leaves everyone miserable when Lucky fails, Luanne reveal she's pregnant and was waiting for his graduation to tell him, and Hank is forced to Shotgun Wedding them when Lucky keeps to the spirit of not marrying her if he stayed a failure, turning Luanne back into the trailer trash lifestyle she tried so hard to escape, and it's all Peggy's fault.
- The Loud House: In “Driving Miss Hazy”, while Leni prepares to take her driving test, Lori, fearing losing her status as the only Loud child who can drive (and the ability to extort favors from her siblings because of it), gives her terrible advice that guarantees she’ll fail the test. However, Lori quickly changes her tune when Lincoln points out that her bad advice could get Leni into an accident, and she races to the DMV to apologize and make sure her sister doesn't hurt herself.
- The Simpsons:
- In one episode, Lisa, jealous of Maggie's recently discovered abnormally high IQ, attempts to put her wrong by teaching her the flashcard "Octogenarian" actually refers to the dog.
- In "A Star is Torn", Lisa joins an American Idol-style talent show with Homer as her manager and songwriter, but after an argument over his Stage Dad methods, Homer quits and begins mentoring the other finalist, Cameron. Come the final, however, it turns out Homer only did this in order to sabotage Cameron, by writing a song for him that made him look like a privileged Jerkass.
Homer: He's about to learn the most important lesson in the music business: don't trust people in the music business.
- In an episode of Spongebob Squarepants, SpongeBob beats out Squidward for a role in a dance because it turns out to be a natural talent. Squidward, envious of this, decides to "take SpongeBob under my wing" and proceeds to train him to exhaustion and show up to steal his role. Then it turns out that it's Squilliam's play, who proceeds to berate and work Squidward just like he did SpongeBob.
- Wimp-Lo from Kung Pow! Enter the Fist isn't actually too far from the truth—some martial art schools really would "train" a student incorrectly if they felt they were unworthy of learning their actual techniques.
- A Brief Synopsis of The Lord of the Rings Subtitled "Your homework done for free!" and you get what you paid for. Notable for having fooled a London Sunday Times reporter.
- Forcing people in your custody to "teach" you things generally ends badly.
- American POWs during the Cold War were often forced to teach enemy spies about how to pass as an American. For example, they might say to NVA agents that the Dead Man's Hand in poker is two pair, kings and jacks (it's aces and eights).
- One account of an American sailor taken captive by the Imperial Japanese Navy describes an abusive IJN officer forcing the narrator to teach him English. For reasons of both personal amusement and spite, he taught him "catastrophically bad English" — one example responding to "How are you?" with "What the fuck do you care?"
- This is a common retaliation against bullies and cheaters on Not Always Learning. Here are examples.
- One (unconfirmed) theory of how the term "Eskimo" originated: explorers in Alaska asked the wrong people what to refer to the Inuit tribes. Instead of asking the fishing-based Inuits directly, they asked land-based hunters, who were enemies of the Inuits. Naturally, these hunters told the explorers they were the "Eskimo", which allegedly means "a person who eats raw meat".