A few fries short of a happy meal.

The wheel's spinning, but the hamster's dead.

All foam, no beer.

The cheese slid off his cracker.

Body by Fisher, brains by Mattel.

Warning: Objects in mirror are dumber than they appear.

He fell out of the stupid tree and hit every branch on the way down.

As smart as bait.

Her sewing machine's out of thread.

One fruit loop shy of a full bowl.

Her antenna doesn't pick up all the channels.

His belt doesn't go through all the loops. 

Proof that evolution CAN go in reverse.

Receiver is off the hook.

Skylight leaks a little.

Her slinky's kinked.

Too much yardage between the goal posts.

Got a full 6-pack, but lacks the plastic thingy to hold them together.

Gates are down, the lights are flashing, but the train isn't coming.

If brains were taxed, he'd get a rebate.

Standing close to her, you can hear the ocean.

Some drink from the fountain of knowledge, but he just gargled.