I think 'stupid' may be rather harsh Archie, you old felon. How about:-
The wheel's spinning, but the hamster's dead.
A few clowns short of a circus.
Thought Chubber Checker's a board game for fatties.
A few fries short of a Happy Meal.
An experiment in Artificial Stupidity.
A few beers short of a six-pack.
A few peas short of a casserole.
Doesn't have all his cornflakes in one box.
All foam, no beer.
Warning: Objects in mirror are dumber than they appear.
Couldn't pour water out of a boot with instructions on the heel.
He fell out of the stupid tree and hit every branch on the way down.
Doesn't know much, but leads the league in nostril hair.
Elevator doesn't go all the way to the top floor.
Forgot to pay his brain bill.
Her sewing machine's out of thread.
His antenna doesn't pick up all the channels.
His belt doesn't go through all the loops.
Missing a few buttons on his remote control.
No grain in the silo.
Proof that evolution can go in reverse.
Receiver is off the hook.
Skylight leaks a little.
Surfing in Nebraska.
But if you think Queen fans are dummies, you should try a peek over at StingZone. They eat bananas with their feet over there.
FLASHMAN STRIKES AGAIN!
Paul Rodgers is not the best thing since fried Fred.