Once you have stated a joke or "pun" and nobody noticed you even talked, the person sitting directly beside you repeats the joke and everybody heard it and he/she gets all the laughs and all the credit for your unique joke.
(You) "Why can't Helen Keller drive a car?...Because she's a woman!!!!"
(Crowd)-----(Didn't acknowledge your existence)----
(Pun-Stealer) "Why can't Helen Keller drive a car?...Because she's a woman!!!!"
(Crowd) "HAHAHAHA!!! He's so funny, if only I were as awesome, unique, witty, and brilliant as he is! I bet all the girls are begging to sleep with him!
(You) "I HATE YOU, YOU FRIGGIN' PUN-STEALER! I WILL EAT YOUR FIRST BORN CHILD!"
A woman with a nice ass that you eventually have sex with after meeting eachother through the multiplayer of any Call of Duty game.
(You) "I got some major Call of Duty Booty last night dude!"
(Friend) "Nice man! You think you can give me her number?"