Here is a not-so-brief list
of different ways to say someone is stupid
from various sources.
Not the sharpest knife in the drawer.
Not the brightest star in the sky.
Not the brightest bulb on the Christmas tree.
A few fries short of a Happy Meal.
About a quart low.
A few bricks shy of a full load.
About as sharp as a bowling ball and half as bright.
About as sharp as a wet burlap sack.
Duller than a used butter knife.
A wit like a steel bear trap: rusty and prone to snapping.
Has it all together, but can never remember where he put it.
The wheel's still turning, but the hamster's dead.
The lights are on, but nobody's home.
The gate is down, the lights are flashing, but the train ain't coming.
See also nice names for stupid people