Generally, You Taught Me That is a StockPhrase directed at a mentor. The pupil is exhibiting, and thankful for, a skill or a value that the mentor taught him, and [[WellDoneSonGuy wants the mentor to be proud of him]].

In a more dramatic use, You Taught Me That is directed at a former mentor, in a situation where the mentor and the pupil find themselves on opposing sides. It could mean one of three things:
# The student defeats the mentor using [[HoistByHisOwnPetard a trick that the mentor had taught him]].
# The student is sticking to the values that the mentor had taught him, before the mentor's FaceHeelTurn. In this case, the mentor is a BrokenPedestal.
# The mentor had been a bad example to the student, usually unintentionally, since the mentor's actions didn't seem to live up to his words. This is what prompted the student's Face Heel Turn, and he is currently exhibiting the same flawed behaviour that his mentor regrets. Expect [[WhatHaveIDone a lot of guilt]] on the mentor's part.
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!!Examples:

* An odd variation in that the "mentor" is consistently villainous: in the [[Film/HarryPotter film]] of ''Film/HarryPotterAndTheOrderOfThePhoenix'' (as in the book), Professor Umbridge makes Harry magically carve the words "I must not tell lies" on the back of his hand as a punishment for telling a CassandraTruth (that Voldemort has returned). Towards the end, he and Hermione have lured Umbridge to a centaur herd, and when Umbridge pleas for Harry to tell the centaurs she means them no harm, he replies "I'm sorry, Professor, but I must not tell lies", while holding up the scarred hand.
** Harry does it again in the seventh film.
* In ''Discworld/{{Mort}}'', an EvilVizier has a plan to poison his emperor but is outmaneuvered by the emperor and has to eat the poison himself. As he's dying he compliments the Emperor on what he's done and the Emperor says "I had a great teacher."
* At the end of ''LawAbidingCitizen'', the villain is finally cornered by the protagonist, a prosecutor who is responsible for starting the whole thing by making a deal with a murderer. When the villain tries to negotiate, the prosecutor says he doesn't make deals with murderers anymore and references this trope.
* ''Series/TheBill''. Inspector Burnside gets a complaint from a judge when a female detective 'accidentally' reads out the accused former offenses in court. When Burnside tells her off for it, she points out that she learned that trick from Burnside.
* The late 80's anti-drug {{PSA}} [[http://en.wikipedia.org/wiki/I_learned_it_by_watching_you! "I learned it by watching you!"]] expresses the third version with a slightly different phrasing.