She was traveling downtown on a bus when a young man bumped into her and said, "Watch it, old lady."
To which she stopped and replied, "Thank you, young man, for calling me an old lady. May you live long enough so that one day someone can call you an old man."
I doubt that boy walked away from that experience feeling very upset with that "old lady" anymore. She could have walked away from that bus, angry. He would have been annoyed. It might have affected both of their days for the worse, but she turned it into something better. Because she saw that he would grow up and love and live and hopefully one day, be an old man with a story.
I think that sometimes it is easy to pass people on the street or in the grocery store or at the post office--absorbed in our own tasks and forgetting that these people are more than just a backdrop to our lives. They have their own story. As writers this is something that we work at understanding. Behind every stranger is a novel, a beautiful masterpiece.