Be on somebody’s case Definition 1 of 2Pro Tip 1/3Negative Implication Implies irritation or annoyance towards someone's behavior or action. Stop being lazy with your chores, or I'll be on your case. Pro Tip 2/3Informal Usage Used in casual situations, rarely in a professional or formal context. If you keep arriving late, your friends might get on your case. Pro Tip 3/3Personal Pressure Indicates personal pressure rather than constructive criticism. Don't be on my case, I already know I made a mistake.