Enter the half-joke, half-serious concept of “silver springing” someone. It’s the idea that you and all the love you bring with you are unforgettable — like a ghost that will eternally haunt them.

Within 10 minutes of the gathering's opening, nearly 100 Bostonians flocked to City Hall Plaza for free Egg McMuffins and coffee Friday to take part in McDonald’s All Day Breakfast Pajama Party, which...