Purim

Purim is the happiest Jewish holiday of the year. During this holiday, people of all ages dress up in costumes and parade throughout the country. Although it is officially celebrated on two days (one for Jerusalem and one for everyone else), the celebrations and happiness lasts for the entire week and even month of Adar. 
Coming from America, it is a huge culture shock to see everyone in costumes having a major party in the streets. I guess in San Francisco it isn't that uncommon, but the reason for celebration and the atmosphere is completely different. In San Francisco people dress up and have major parties in the street during the Bay to Breakers Marathon. During Purim, people actually have purpose to their weirdness and happiness and it is not just to fill a day of the year. There are certain customs that come with celebrating a national holiday such as reading the Megillah, sending Mishloah Manot, and eating Hamentashen. This holiday is so special, there are no words to describe the happiness and joy. It is simply a holiday to experience for yourselves.