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.