slang 1. To lose one's temper. When that pushy salesman came back Mom really flipped her lid.
Compare: BLOW A FUSE. 2. To lose your mind; become insane. When he offered me three times the pay I was getting, I thought he had flipped his lid. 3. To become unreasonably enthusiastic. She flipped her lid over a hat she saw in the store window. He's flipped his lid over that new actress.