not know (one's) ass from a hole in the ground

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not know (one's) ass from a hole in the ground

rude slang To be exceptionally stupid, naïve, or dimwitted. I'm not surprised to hear that she got lost two blocks away from her house—she doesn't know her ass from a hole in the ground. Our prime minister wouldn't know his ass from a hole in the ground, so why do we think that he'll handle this negotiation with any amount of success?
See also: ass, ground, hole, know, not
Farlex Dictionary of Idioms.

know one’s ass from a hole in the ground

tv. to be knowledgeable; to be alert and effective. (Usually objectionable.) That stupid son of a bitch doesn’t know his ass from a hole in the ground.
See also: ass, ground, hole, know

not know one’s ass from a hole in the ground

tv. not to be knowledgeable; not to be alert and effective. (Usually objectionable.) That stupid son of a bitch doesn’t know his ass from a hole in the ground.
See also: ass, ground, hole, know, not
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • a plain Jane
  • appear to
  • a change of heart
  • a shoulder to cry on
  • a mystery to (one)
  • be (on) the wrong side of (an age)
  • be on the right/wrong side of 40, 50, etc.
  • a turn of phrase
  • able to do
  • able to do it