"My Leg" is a quote from the Fanon Death Battle, Finn and Jake VS Shrek and Donkey. The foght was created by the user Death batle on May 31st 2015. The quote was said after Finn the Human stabbed Shrek in the leg with his Demon sword.
The quote is often said by Hipper and 5555thExplosionMage. Sadly, it's unknown when the meme started