I got you and Leonard a few silly neighbor-gifts, so I'll just put them under my tree. –Wait! You bought me a present? –Uh-huh. –But why would you do such a thing? –I don't know, 'cause it's Christmas? –Oh, Penny! I know you think you're being generous, but the foundation of gift-giving is reciprocity. You haven't given me a gift. You've given me an obligation.