doesn't/wouldn't know (one's) ass from (one's) elbow(redirected from don't know their ass from their elbow)
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doesn't/wouldn't know (one's) ass from (one's) elbow
rude slang Is very stupid 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 her elbow.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.