Put-downs Galore!

Not the sharpest knife in the drawer.
Got into the gene pool while the lifeguard wasn't watching.
A room temperature IQ.
Got a full 6-pack, but lacks the plastic thingy to hold them together.
A gross ignoramus -- 144 times worse than an ordinary ignoramus.
A photographic memory, but the lens cover is glued on.
A prime candidate for natural deselection.
Bright as Alaska in December.
One celled organisms out-score him in IQ tests.
Donated his body to scientists... Before he was done using it.
During evolution his ancestors were in the control group.
Fell out of the family tree.
Gates are down, the lights are flashing, but the train isn't coming.
Has two brains; one is lost and the other is out looking for it.
He's so dense, light bends around him.
If brains were taxed, he'd get a rebate.
If he were any more stupid, he'd have to be watered twice a week.
If you give him a penny for his thoughts, you get change back.
If you stand close enough to him, you can hear the ocean.
One neuron short of a synapse.
Some drink from the fountain of knowledge, but he just gargled.
Takes him an hour and a half to watch "60 Minutes".
Was left on the Tilt-A-Whirl a bit too long as a baby.
Wheel is turning, but the hamster is dead.