The middle-aged white lady at a low-budget store (think Walmart) who mistakes you for an employee, then threatens to "have you fired" when you won't do your job. The only way to stop her is by calling Security or the police and having her physically removed from the store.
Yesterday a Karen thought I worked at the store where I was stopping and wanted me to do HER shopping. When I refused she started screaming and Security had to drag her sorry ass out the door and ban her for life!