what for
1. Why? For what reason? A: "You're both in deep trouble." B: "What for? We didn't do anything." A: "We'll have to stop by the grocery store on the way home." B: "What for?" A: "We need milk and eggs."
2. A scolding, rebuke, or punishment. Sometimes hyphenated. My grandmother wouldn't hesitate to give me what for when my parents weren't around. The boss is quick to give you the what for if you make even a minor mistake.