Purim

Purim marks the events in the Book of Esther, when the Persian official Haman planned to wipe out the Jews of the empire and Queen Esther talked King Ahasuerus out of it. It's celebrated with costumes, noisemakers to drown out Haman's name during the reading, gifts of food to friends and to the poor, and a meal that runs long. It's also the one holiday where getting a little drunk is a stated part of the tradition, which tells you something about how relieved everyone was.