know as much about as a hog knows about Sunday

know as much about something as a hog knows about Sunday

Rur. to have no knowledge of something. Don't let Jim make dessert for the picnic. He knows as much about pies as a hog knows about Sunday. I had quite a time changing the tire, since I know as much about cars as a hog knows about Sunday.
See also: hog, know, much, Sunday