know from nothing
not know from nothing
To be completely ignorant or uninformed (about something). Don't ever second-guess my judgment again, you hear me? You don't know from nothing! Don't mind her, Phil. She doesn't know from nothing.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
know (or not know) from nothingbe totally ignorant, either generally or concerning something in particular. North American informal
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