(I work at a self-serve frozen yogurt shop, where people get their own yogurt and toppings then pay by weight.)

Customer: “Excuse me, you should be supervising this store. These kids are putting their fingers in the toppings. It’s not clean!”

(I look around for a parent, but there seems to be nobody else of suitable age in the shop.)

Me: “Are these your children?”

Customer: “Yes, but you should be supervising them! It’s your job!”