For little ghetto kids who aren't old enough to call people jack a@s yet, there is jack monkey. A perfectlyacceptable synonym which prevents a whoopin for using a bad word.
1. An unfathomable moron
The word JackMonkey was origonally a derivative of "jack off" that was created in a moment of absolute frustration. The defining factor of a JackMonkey is their inability to grasp even the simplest concepts that are new to them.
I tried to teach that JackMonkey to tie his shoes but all he managed to do was get his fingersstuck in knots.