Purim reminds us that we live in an olam hafuch, an upside-down world. To wit, in the book of Esther Mordecai rises to the position occupied by Haman, while Haman hangs from the gallows built for Mordecai, and the doom decreed for the Persian Jews is visited upon their enemies.
On Purim we embody this upside-down world. Men dressing as women! Students teasing their teachers! Wild revelry prevailing in usually dignified places.