the back of (one's) hand(redirected from back of their hands)
the back of (one's) hand
1. A rejection, snub, or rebuke; a display of contempt or scorn for someone or something. She met their accusations with the back of her hand. I give the back of my hand to anyone who says I'm not a good parent.
2. Used to represent one's complete knowledge of or familiarity with something. Usually used after the verb "know." I've read this book so many times, I know it like the back of my hand. You should ask Samantha for directions—she knows this town like the back of her hand.
back of one's hand
Rejection or contempt, as in Unimpressed with him, she gave the back of her hand to his suggestion. This phrase is usually the object of a verb such as give or show. [Second half of 1700s] Back of the hand similarly means "an insult" in the term back-handed compliment (see under left-handed compliment) but has a quite different meaning in know like the back of one's hand (see under know like a book).