not know (one's) head from (one's) tail

not know (one's) head from (one's) tail

To be exceptionally stupid, naïve, or dimwitted. I'm not surprised to hear that she got lost two blocks away from her house—that girl doesn't know her head from her tail. We thought we were electing a prime minister who was in touch with the common people, but instead we elected a fool who doesn't know his head from his tail.

See also: head, know, not, tail

Farlex Dictionary of Idioms. © 2024 Farlex, Inc, all rights reserved.