not 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.
See also: know, not, nothing
Farlex Dictionary of Idioms.

not know from nothing

Inf. to be stupid, innocent, and naive. (This nothing is not replaced with something. Usually used with don't, as in the examples.) Old John—he don't know from nothing. What do you expect from somebody who don't know from nothing?
See also: know, not, nothing
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

know (or not know) from nothing

be totally ignorant, either generally or concerning something in particular. North American informal
See also: know, nothing
Farlex Partner Idioms Dictionary

not know from nothing

in. to be stupid, innocent, and naive. (see also know from something.) Tom don’t know from nothing. He is really dense.
See also: know, not, nothing
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • doesn't know beans
  • come it
  • come it (with one)
  • all in (one's) head
  • (I) don't mind if I do
  • don't get me wrong
  • a sob story
  • don't bet on it
  • don't give up the ship
  • don't beat a dead horse