You...
...are a few fries short of a happy meal.
...are a few wheels short of a bycycle.
...are a few buttons short of a remote control.
...are not the brightest bulb on the Christman Tree.
...are not the brighest crayon in the box.
...got a negavite number of your SATs.
...are dumber than a bag of rocks.
...are not the sharpest hunk of cheese.
...got too much chorine in your gene pool.
...are a few peas short of a casserole.
...are dumber than a box of hair.
...are a taco short of a combo plate.
...are about as sharp as a bowling ball.
...are not the quickest tractor on the farm.
...are not welcome at the Star Trek convention.
The room temperature is higher then your I.Q.
If you were any dumber, we would have to water you twice a week.