don't try to explain it to him fellas, the lights are on but no one is home...
in other words
the elevator don't reach the top floor
a few slices short of a loaf
a few bottles shy of a six pack
he is as sharp as a bowling ball
he is as smart as a bag of rocks
that puddle of sludge is slicker then him
these are not to you scorp just different ways of saying someone is "intellectually handicapped"