not know the first thing about (something)

not know the first thing about (something)

To not know anything about (something). I don't know the first thing about computers, so you'll have to explain this to me really slowly. What's an attachment again? Geoff wouldn't know the first thing about how to take care of a baby. Thank goodness Frank is there to help babysit.
See also: first, know, not, thing

not know the first thing about someone or something

Fig. not to know anything about someone or something. I don't know the first thing about flying an airplane. She doesn't know the first thing about John.
See also: first, know, not, thing
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