Actual lines out of U.S. Military OERs (Officer Efficiency Reports) and from Royal Navy and Marines officer fitness reports:

A gross ignoramus = 144 times worse than an ordinary ignoramus.
A photographic memory but with the lens cover glued on.
A prime candidate for natural de-selection.
A room temperature IQ.
Bright as Alaska in December.
Donated his body to science before he was done using it.
Fell out of the family tree.
Gates are down, the lights are flashing, but the train isn't coming.
Got a full 6-pack, but lacks the plastic thingy to hold it all together.
Got into the gene pool while the lifeguard wasn't watching.
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'd get change.
If you stand close enough to him, you can hear the ocean.
It's hard to believe that he beat out 1,000,000 other sperm.
Not the sharpest knife in the drawer.
One neuron short of a synapse.
One-celled organisms outscore him in IQ tests.
Some drink from the fountain of knowledge; he only gargled.
Takes him 10 hours to watch 60 minutes.
This medical officer has used my ship to carry his genitals from port to port, and my officers to carry him from bar to bar.
Was left on the Tilt-A-Whirl a bit too long as a baby.
Wheel is turning, but the hamster is dead.