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/
1.
一竅不通, 笨手笨腳
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.
他太無能了，簡直一竅不通。
•
Don't ask him for help; he doesn't know his ass from his elbow when it comes to computers.
別向他求助；他對電腦簡直一竅不通。