Not Too Bright...

Not the sharpest knife in the drawer.
Got into the gene pool while the lifeguard wasn't watching.
She's from the shallow end of the gene pool.
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 prime candidate for natural deselection.
Bright as Alaska in December.
Nearly as bright as a one celled organism.
Donated his body to scientists... Before he was done using it.
Gates are down, the lights are flashing, but the train isn't coming.
He's so dense, light bends around him.
If brains were taxed, she'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 her, you can hear the ocean.
One neuron short of a synapse.
Some drink from the fountain of knowledge, but she just gargled.
Takes him 1.5 hours 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.