cut somebody to the quick
cut (one) to the quick
1. To slice a part of the body very deeply. Be careful—one slip of that knife and you'll cut yourself to the quick.
2. To strike the deepest, most fragile part of one. Typically used to describe emotional wounds. I can't even look at her right now—that hurtful remark cut me right to the quick.
cut somebody to the ˈquickhurt somebody’s feelings; offend somebody deeply: It cut her to the quick to hear him criticizing her family like that.
The quick is the soft, sensitive flesh that is under your nails.