know which end is up

not know which end is up

To be especially naïve, dimwitted, or uninformed. Give her a break—I didn't know which end was up when I was her age either. Local officials don't know which end is up when it comes to dealing with the housing crisis.
See also: end, know, not, up
Farlex Dictionary of Idioms.

know which end is up

tv. to be alert and knowledgeable. Don’t try to hustle me, sister. I know which end is up.
See also: end, know, up
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • (my) mama didn't raise no dummy
  • dummt
  • dummy
  • (my) momma didn't raise no dummy
  • as we know it
  • a closed book
  • closed book, a
  • I know
  • (I) can't say as I do
  • can't say as I do