Oh! You have hit on a thing I love to do (not always, but when the time is right). I will turn to you, random stranger behind me, to make a humorous observation as though we know each other, because we are In This Together (the grocery line). Especially if someone is breaking the agreed-upon grocery store code of ethics/etiquette in some way. (Or if I just think of something clever, and I need to tell someone before I pop). A good stranger interaction is peak, and I indeed take this as a high compliment.