Flippy Cup

(My sister has been the only one home for several days. When I go to get a cup from the cupboard, they are all flipped upside down.)

Me: “Why are all the cups like this?”

Sister: “I don’t know.”

Me: “How could anyone else have done it? You didn’t have friends over, did you?”

Sister: “No, I did it. I just don’t know why.”