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.