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).