1. Not the sharpest knife in the drawer.
2. Got into the gene pool while the lifeguard wasn't watching.
3. A room temperature IQ.
4. Got a full 6-pack, but lacks the plastic thingy to hold them together.
5. A photographic memory, but the lens cover is glued on.
6. A prime candidate for natural de-selection.
7. Bright as Alaska in December.
8. During evolution, his ancestors were in the control group.
9. Fell out of the family tree.
10. Gates are down, the lights are flashing, but the train isn't coming.
11. Has two brains; one is lost and the other is out looking for it.
12. He's so dense, the light bends around him.
13. If he were any more stupid, he'd have to be watered twice a week.
14. If you stand close enough to him, you can hear the ocean.
15. It's hard to believe that he beat 100,000 other sperm.
16. Some drink from the fountain of knowledge, but he just gargled.
17. Takes him a hour-and-a-half to watch "60 Minutes".
18. One burger short of a happy meal.