wouldn't know (something) if it hit (one) in the face

wouldn't know (something) if it hit (one) in the face

Is too oblivious or ignorant to realize or recognize a very obvious thing. You're no expert. You wouldn't know a Rembrandt if it hit you in the face. Tim's not much of a scout. He wouldn't know promising talent if it hit him in the face.
See also: face, hit, if, know
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