touch a sore spot
touch (on) a sore spot
To evoke a strong and negative emotional reaction in someone; to do or say something that upsets someone in a deeply personal way. Your column must have touched a sore spot with readers, because we are getting slammed with negative feedback. I could tell he was touching on a sore spot, because Jane went deathly silent when he brought up her former employer.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
touch a sore spotand touch a sore point
Fig. to refer to a sensitive matter that will upset someone. (Fig. on the notion of touching an injury and causing pain.) I seem to have touched a sore spot. I'm sorry. I didn't mean to upset you. When you talk to him, avoid talking about money. It's best not to touch a sore point if possible.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.