doesn't/wouldn't know (one's) arse from (one's) elbow

(redirected from know arse from elbow)

doesn't/wouldn't know (one's) arse 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 arse from her elbow.
See also: arse, elbow, know