Yes, the megaphone was attached to a podium that said "Say Something Nice", but you half expect some New York jackass to hijack the megaphone and curse everybody out (maybe it was edited out!). But seriously, watching this will brighten up your Monday.
It was a stunt pulled by the lovely folks of Improv Everywhere: they wheeled a megaphone and podium into Union Square and just left it there. Once people noticed it, they jumped at the chance to address the crowd. My personal favorite: when the little boy says "To Infinity and Beyond".