That should serve as a lesson not to do something! Said when one receives some fitting punishment or negative outcome as a result of their actions. (The meaning is the same regardless or whether "not" is used.) My men are going round to rough the accountant up. That'll teach him to go talking to the police. A: "She's been sentenced to 10 years in prison for her involvement in the scam." B: "Good. That'll teach her." A: "Ouch! You hit me in the head!" B: "That'll teach you not to talk back to me!"