In wrestling: a jobber.
In reality: Dumbass. Loser. A no good son of bitch. Talks a lot of shit but can never back it up.
Calvin: Do wanna pick up some McDonald’s?
Kiff: Sure
*gets to McDonald’s*
Calvin: Dude I forgot my wallet, can you pay for me?
Kiff: you’re a fucking jabroni
Jack blacks online ID is jablisnkigames so a popular wide term Saying is get Jablinskified when you kill someone in a game. Popularised by Scameron (Mr moo moo and the OCE bombers)