Not the brightest star in the sky.
The light's on but no one's home.
Not the brightest bulb in the box.
A few screws short of a hardware store.
Not the sharpest knife in the drawer.
A few cards short of a full deck.
A few fries short of a Happy Meal.
About as sharp as a marble.
Only has one oar in the water.
Smart as a bag of rocks.
A hamburger short of picnic.
The elevator doesn't go all the way to the top floor.
A few peas short of a casserole.
A few keys short of a piano.
Not the brightest bulb on the Christmas tree.
The gates are down and the lights are flashing, but the train isn't coming.
As smart as a stick.
Fell out of the stupid tree and hit every branch on the way down.
An intellect rivaled only by garden tools.
Has an IQ of room temperature.
Couldn't pour water out of a boot with instructions on the heel.
Not the sharpest crayon in the box
Not the the sharpest tool in the shed
They are depriving some village of its idiot.
A few threads short of a sweater.
Driveway doesn't quite reach the road.
The battery is not fully charged.
Dumber than a bag of hammers.
A few bricks short of a full load.
A few clowns short of a circus.
A few beers short of a six-pack.
Dumber than a box of hair.
All foam no beer.
As smart as bait.
Forgot to pay his brain bill.
The antenna doesn't pick up all the channels.
Missing a few buttons on his remote control.
Proof that evolution CAN go in reverse.
Receiver is off the hook.
Has a leak in the skylight.
Too much yardage between the goal posts.
Not all the soldiers are marching in line.
Dumber than paint.
Half a bubble off plumb.
Donated his brain to science before he was done with it.
A few shades beyond blonde.
A few watts short of a light bulb
Running on 3 cylinders.
Has the parachute but is missing the ripcord.
Would lose a debate with a doorknob.
Has an IQ lower than plant life.
All volume, and no content.
Wouldn't know if they were on foot or horseback.
The wheel is spinning but the hamster is dead.
The cheese slid off the cracker.
Doesn't have all the chairs at the table. .
A shining example of why you should avoid inbreeding.
A few pecans short of a fruitcake.
Would argue with a signpost.
If you gave them a penny for thoughts, you'd get change.
Dumb as a salt shaker.
Has a mind like a steel trap: rusty and illegal in 37 states.
Knitting with only one needle.
The result of too much chlorine in the gene pool.
Not the quickest bunny in the forest.
The hard drive is spinning but the OS hasn't been installed.
Not exactly burning all thrusters.
A few colors short of a rainbow.
The boat doesn't have all the oars in the water.
A few ships short of a fleet.
A monosynaptic cretin (Don't understand it? 'nuff said)
A few noodles short of a chow mein.
A few bristles short of a broom.
Doesn't know whether to scratch his watch or wind his butt.
Hasn't seen the ball since kickoff.
The relative IQ of a deck chair.
A poster child for birth control.
A few players short of a team.
Couldn't hit the floor if he fell on it.
A few sheep short of a flock.
Not the brightest light in the harbor.
One plate short of a tea set.
A few kangaroos loose in the top paddock.....
A few slices short of a sandwich.....
A few sausages short of a BBQ
If her IQ was any flipping lower we'd have to water her.
A few more braincells and he would be a cabbage