dumb as a post

Dumb as a post is an idiom which insults the intelligence of someone and compares them to an inanimate object that would obviously have no intelligence; in this case, they are compared to a post, or a fencepost. Dumb as a post is simply another way to explain just how unintelligent (stupid or dumb) somebody is whether it is lack of intelligence or a response to something they did with no common sense.