A few clowns short of a circus.

A few fries short of a Happy Meal.

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.

All foam, no beer.

The cheese slid off his 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.

Smart as bait.

Her sewing machine's out of thread.

His belt doesn't go through all the loops.

No grain in that silo.

Skylight leaks a little.

Surfing in Nebraska.

Too much yardage between the goal posts.