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1.
a dum person who just keeps getting dumber
my boyfriend
by linda rondstat August 10, 2003
 
2.
A dumb person who just keeps getting dumber.

As heard on the Rush Limbaugh show, which gave a shout-out to Urban Dictionary regarding this word.
Ardent John Kerry supporters are a bunch of jackballs!
by Hyacinth Bucket December 30, 2004
 
3.
knucklehead, fool, dummy, idiot, moron; depending upon the context.

Jackball is word for which the meaning is subjective and entirely related to the user's state of mind. It ranges from the 'knucklehead' to the 'idiot' or 'moron' end of the scale depending upon whom you are referring.
Example: When addressing a friend it is more likely meant in the 'knucklehead' sense. If you were driving down the road and some manic cuts you off or you're watching TV and Bush is trying to complete a sentence or pronounce the name a of a foreign dignitary and you yell, "JACKBALL!" Clearly, it is being employed in the 'idiot' or 'moron' sense.
by Jackball Hansen March 21, 2006
 
4.
Used to describe anyone sitting on their ass not doing a damn thing, just like a Jack ball you would get from Jack in the box.
"Look at those Jack balls, here we are working and those idiots are playing grab ass"
by Big Wobblers November 03, 2006
 
5.
Can be used as a verb, meaning the deliberate act of taking or stealing. A jackball is a small "victory" for the jackballER and an annoyance to the jackballEE. It can often be advantageous for the jackballER to appear unaware of the jackball if noticed or confronted.
That lady jackballed my spot in line!

If this guy gets up, jackball his seat.
by n8dizzle November 21, 2006
 
6.
Describes a person of either sex who does nothing. Basically contributes absolutely nothing of redeeming quality to the world around them. The word and subsequent definition came about after witnessing a person installing a Jack in the box jack ball on their antenna and asking myself what the hell does that damn thing do? Nothing!
Hey there's Don V doing what he does best, acting like a Jack Ball just sitting there on his fat ass. I bet he took Jack Ball lessons from Cait.
by Pig Slapper May 20, 2007