DOESN'T KNOW HIS ASS FROM A HOLE IN THE GROUND
doesn't know his ass from a hole in the ground: translation
doesn't know his ass from a hole in the ground & doesn't know his ass from his elbow
doesn't know anything; acts ignorant. (Use
ass
with caution. Also with
don't
.
Don't
used with all persons is folksy.) •
That teacher doesn't know his ass from a hole in the ground.
•
She's supposed to be an expert, but she doesn't know her ass from her elbow.