Mine - Its not that great but whatever - I taught myself a language through song translation.
I was heavily into German Rock music while I was in highschool, and I would translate the non-English songs for fun, with google. By graduation, I was almost able to speak the language. Not fluently, but I got by from the people I knew who actively spoke the language.
Its been 6 years and Im not even interested in the music anymore, maybe from constant repetition of the same 4 albums over and over.
Anyway, Whats yours?
Something I've taught myself:
-At the risk of sounding meta, I taught myself how to tech myself. I found things that motivate me, and use them as rewards for learning things I find boring. This, along with self control, has been the single most important skill I've ever developed.
Something I've done:
-I quit smoking a pack a day, and it stuck. Its odd to think of it now, but I managed to turn a nasty habit into a sense of confidence in my own willpower. I still wish I never started though. The cravings never really leave.