not know your arse from your elbow
成語所屬單字elbow
not know your arse from your elbow — 慣用語
1. To be very stupid or lack basic skill or knowledge.
1.慣用語
釋義
一竅不通；非常愚蠢
To be very stupid or lack basic skill or knowledge.
例句
That mechanic doesn't know his arse from his elbow.
How can she be a doctor if she doesn't know her arse from her elbow?