He doesn't know his ass from his elbow — Он набитый дурак That old bastard don't know his ass from a hole in the ground — Этот тип настоящий придурок
NOT KNOW ONE'S ASS FROM ONE'S ELBOW ETC
Англо-русский перевод NOT KNOW ONE'S ASS FROM ONE'S ELBOW ETC
New English-Russian dictionary of modern informal English. Новый Англо-Русский словарь современного неформального английского. 2012