Sabotutor

"You must excuse Wimp Lo... he is an idiot. We have purposely trained him wrong as a joke."

—Master Tang, Kung Pow! Enter the Fist

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.

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 does this as a joke; or maybe Bob's just an asshole. Whatever happens, you can be sure hilarity will ensue.

This doesn't have to just be a tutor in the academic sense, but any time somebody is instructing another person in a subject.

Examples of Sabotutor include:

Fan Works

This is a common plot device used in Naruto fanfiction. Naruto's lack of skills are 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.

Film

The above-mentioned Wimp Lo from Kung Pow! Enter the Fist is a result of this.

Wimp Lo: "I am bleeding! Making ME the victor!"

Literature

Harry Potter suspects Snape of this when Snape teaches him Occlumency. He was wrong: turns out Harry's just really bad at Occlumency.
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.

Live-Action TV

In Grounded For Life, Sean deliberately "torpedoes" Lily when teaching her how to drive.
In one episode of Scrubs, Dr. Cox has a German patient and 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."
- As another example, Carla tells The Todd phrases in Spanish. Once, when he asks her for a pickup line, she teaches him "I have genital herpes... for you!"
On Married... with Children, Bud did this to Kelly, mainly just 'cause it was funny.
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 to get the user in trouble.
- It's a trope namer.

Newspaper Comics

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: This is an elm tree. Someday it will grow into a mighty oak. You can tell how old it is by counting the leaves.

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.
At least two times in Tank McNamara, 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."

Video Games

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 showing himself as evil.
From the Street Fighter mythos: While training Dan, 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.

Web Original

Professor Steve pulls this off in the Professor Brothers short The Substitute.

Western Animation

In an episode of The Simpsons, 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.
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.
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 early outlines for Avatar: The Last Airbender, Iroh was this to Zuko, under orders from Fire Lord Ozai. By the end of the first season, though, his personality became more well-defined.

Real Life

Most Popular Chinese Tattoo Symbols. Totally not a prank.
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.