A few fries short of a Happy Meal
One beer short of a six-pack
One taco short of a combo
All foam, no beer
An intellect rivaled only by garden tools
Chimney's clogged
Elevator doesn't go to the top floor
His antenna doesn't pick up all the channels
If you had another brain, it'd be lonely
No grain in the silo
Proof that evolution can go in reverse
Slinky's kinked
The wheel's spinning but the hamster's dead