I love a good metaphor. It's almost a requirement to growing up in the south, like brown liquor and pig races. I try to work at least one of them into casual conversation every day. It isn't as hard as you might think, especially on Mondays. Here are some of my favorites with a few regular but awesome insults thrown in as a bonus. You never know when you might need one.
He's as sharp as a bowling ball.
He's all hat, and no cattle.
When I think of all the people I respect the most, you're right there, serving them drinks.
The wheel's spinning, but his hamster's dead.
She couldn't pour water out of a boot with instructions on the heel.
He doesn't have all his dogs on one leash.
He would be out of his depth in a parking lot puddle.
She's got a photographic memory but with the lens cover glued on.
If brains were taxed, he'd get a rebate.
If she were any more stupid, she'd have to be watered twice a week.
When his IQ reaches 50, he should sell.
Her slinky is kinked.
Have a great day!