1. Joan was upset with Bill and she told him just what she thought of him. She really gave him a piece of her mind.
2. I can’t believe that they let their dog loose in my garden. I’m going over there right now to tell them that if I find that dog in my yard again, I’ll call the police. I’m going to give them a piece of my mind!

Synonyms: read (someone) the riot act; chew (someone) out; rake (someone) over the coals; speak (one’s) piece.