A room temperature IQ
A few sandwiches short of a picnic
A one-bit brain with a parity error
A tower short of a castle
A few beers short of a six-pack
As bright as a nightlight
As happy as if he had brains
Batteries not included
Been playing with the pharmacy section again
Contributes to the population problem
Doesn't have all his cornflakes in one box
Forgot to pay his brain bill
Hasn't got all his china in the cupboard
Having a party in his head, but no one else is invited
He's not stupid; he's possessed by a retarded ghost
Her memory is truly random-access
His antenna doesn't pick up all the channels
His buffer is full
His puzzle is missing a few pieces
Missing a few buttons on his remote control
Not enough brains cells for the Prozac to be effective
Not enough change to break a dollar
Not firing on all eight cylinders
Not the sharpest knife in the drawer
Not the shiniest penny in the fountain
Not the pointiest quill on the porcupine
Not the brightest bulb on the Christmas tree
Nutty as a fruitcake
One bit short of a byte
One sentence short of a paragraph
Only playing with 51 cards
Only playing with the jokers
Permanently rotated 90 degrees from the rest of us
Proof that evolution *can* go in reverse
Skating on the wrong side of the ice
So slow he has to speed up to stop
Sort of like an inverse Einstein
Source code is missing a few lines
Suffers from Clue Deficit Disorder
Swimming in the shallow end of the gene pool
Thinks in lower case and types accordingly
Unclear which of Newton's three laws of motion keeps his ears apart
Vacancy on the top floor