not know beans

Also, not know the first thing; not know from nothing. Be ignorant about something, as in a poem published in the Yale Literary Magazine in 1855: “When our recent Tutor is heard to speak, This truth one certainly gleans, ������ever he knows of Euclid and Greek, In Latin he don't know beans.” The beans in this colloquial phrase, dating from the early 1800s, signify something small and worthless; not knowing the first thing about something clearly shows one doesn't know anything about it at all; and the third slangy phrase, with its double negative, implies stupidity as well as ignorance, as in Poor girl, just starting out and she doesn't know from nothing.