A few ways to say someone is Stupid / weird / not all there...

A few clowns short of a circus.

A few fries short of a Happy Meal.

A few beers short of a six-pack.

A few peas short of a casserole.

Doesn't have all her cornflakes in one box.

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

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.

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

Chimney's clogged.

Doesn't have all his dogs on one leash.

Elevator doesn't go all the way to the top floor.

Forgot to pay her 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.

Missing a few buttons on his remote control.

Receiver is off the hook.

Several nuts short of a full pouch.

Slinky's kinked.

Too much yardage between the goal posts.

Not the sharpest knife in the drawer.

The lights are on, but nobody's home.

Some of these are pretty good! I love the bold ones..