dumb as a post

(as) dumb as a post

Very stupid. You took apart the entire washing machine just to unblock the pump? I swear, sometimes you can be as dumb as a post, Larry. I used to think that kid was dumb as a post, but he turned out to be a physicist.
See also: dumb, post
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

dumb as a post

AMERICAN, INFORMAL
If you describe someone as dumb as a post, you mean that they are very stupid. She's one of the most famous physicists in the country, and she's dumb as a post!
See also: dumb, post
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012
See also: