show (someone) the back of (one's) hand
1. To strike someone with the backside of one's open hand. Son, I'll show you the back of my hand if you ever speak to your mother that way again.
2. To reject, snub, or rebuke (someone); to display contempt, scorn, or rejection (to or for someone). I'll show the back of my hand to anyone who says I'm not a good parent. He pleaded to be forgiven by his wife, but she merely showed him the back of her hand.