What does Margo do to Lacey?

Margo takes Q to her best friend Lacey's house. Lacey hadn't told her about Jase, which made her a terrible friend. Margo explains how Lacey would belittle Margo's appearance and then Margo fishes for compliments from Q, who is happy to give them to her. When they arrive at Lacey's, Margo jimmies open the door to Lacey's car and leaves a fish inside and a note that their friendship "sleeps with the fishes." She then spray paints an M on the top of her car.