OK, let's all say this together. Cinco de Mayo is not Mexican Independence Day, which is in September.
Cinco de Mayo commemorates the 1862 victory of the Mexican army over French forces in the Battle of Puebla and is celebrated more widely in the United States than in Mexico. In fact, the first real Cino de Mayo fiestas were thrown in California, not Mexico, and the holiday has always been a largely American phenomenon.
Even so, that's no reason not to celebrate San Francisco's Mexican heritage--in ways ranging from relatively authentic to pretty much the opposite of that--with style.
Check out this handy guide we've put together featuring some of the best Cinco de Mayo events the city has to offer. If you have any other suggestions about how to celebrate, leave them in the comments: