back of one's hand, to give (someone) the

back of one's hand, to give (someone) the

To show contempt, to insult. “Here’s the back of my hand to you,” wrote Jonathan Swift (1738), perhaps signifying a challenging farewell. The back of the hand, of course, consists of knuckles, so the expression may once have meant a punch. Similarly, a backhanded compliment is actually malicious in intent.
See also: back, give, of