A simpleton, fool, full retard, or idiot. Origin: "Tropic Thunder" movie by Ben Stiller.
"Don't mind that boy and his foolish mistakes. He can't help it; he's just a Simple Jack."
A movie in tropic thunder, in which ben stiller goes full retard hence simple jack.
Save Simple Jack. Save the retards
"Once upon a time ... there was a retard."
"You went full retard, man" Robert Downey Jr.
To not pull off a retarded impersonation.
To look retarded trying to 'look retarded'
Dude 1: Hey, did you see that guy's retarded impersonation? I totally was not impressed.....
Dude 2: Yeah.. he was going full retard..
Dude 1: ......Simple Jack status...