When you, the 'joker', privately make a hilarious joke at school, work, or in a group of friends and the 'jokee' then passes it on to others, or merely says it louder than you, thus giving the impression that they were the original creator of the joke.
*(Dude 1 whispers hilarious joke..)
Dude 2: HAHAHAHA Hey everyone!
I've got a hilarious joke!!
Dude 1: Hey wat gives?? Why u joke-jacking??