About as sharp as a marble.
A few clowns short of a circus.
Not the brightest bulb on the Christmas Tree.
A few fries short of a Happy Meal.
I wish I had a blueprint for his brain; I'm trying to build an idiot.
An experiment in Artificial Stupidity.
He only has one oar in the water.
A few peas short of a casserole.
Doesn't have all her cornflakes in one box.
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 her cracker.
Body by Fisher, brains by Mattel.
Couldn't pour water out of a boot with instructions on the heel.
An intellect rivaled only by garden tools.
As smart as bait.
Chimney's clogged.