not know your ass from your elbow

US /nɑt noʊ jʊər æs frəm jʊər ˈɛl.boʊ/
UK /nɑt noʊ jʊər æs frəm jʊər ˈɛl.boʊ/
"not know your ass from your elbow" picture
1.

no saber distinguir el culo del codo, no saber nada

to be very stupid or ignorant; to lack basic knowledge or common sense

:
He's so incompetent, he doesn't know his ass from his elbow.
Es tan incompetente que no sabe distinguir el culo del codo.
Don't ask him for help; he doesn't know his ass from his elbow when it comes to computers.
No le pidas ayuda; no sabe distinguir el culo del codo cuando se trata de ordenadores.