A few clowns short of a circus.
A couple of degrees off plumb.
A few fries short of a Happy Meal.
An experiment in Artificial Stupidity.
A few beers short of a six-pack.
Dumber than a box of hair.
A few peas short of a casserole.
Doesn't have all his cornflakes in one box.
The wheel's spinning, but the hamster's dead.
One Fruit Loop shy of a full bowl.
One taco short of a combination plate.
A few feathers short of a whole duck.
All foam, no beer.
The cheese slid off his cracker.
Body by Fisher, brains by Mattel.
Has an IQ of 2, but it takes 3 to grunt.
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
An intellect rivaled only by garden tools.
As smart as bait.
Chimney's clogged.
Doesn't have all his dogs on one leash.
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.
If he had another brain, it would be lonely.
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.
Not the sharpest knife in the drawer.
Not the brightest bulb in the package.
Several nuts short of a full pouch.
Skylight leaks a little.
Slinky's a little kinked.
Surfing in Nebraska.
Too much yardage between the goal posts.
If they took his brain, enlarged it a thousand times and put it on a razor blade, it'd look like a pea on a four-lane highway.