Why is it holiday? I only remember Elaine (from Seinfeld) going into a store called like that
Cinco de Mayo—or the fifth of May—commemorates the Mexican army's 1862 victory over France at the Battle of Puebla during the Franco-Mexican War (1861-1867). A relatively minor holiday in Mexico, in the United States Cinco de Mayo has evolved into a celebration of Mexican culture and heritage, particularly in areas with large Mexican-American populations. Cinco de Mayo traditions include parades, mariachi music performances and street festivals in cities and towns across Mexico and the United States. http://www.history.com/topics/cinco-de-mayo
Several of my Mexican friends tell
me that this is more celebrated in the US than Mexico.
It's more of a holiday to honor the Mexican heritage of Americans
In the United States, Cinco de Mayo is widely interpreted as a celebration of Mexican culture and heritage, particularly in areas with substantial Mexican-American populations. Chicano activists raised awareness of the holiday in the 1960s, in part because they identified with the victory of indigenous Mexicans over European invaders during the Battle of Puebla. Today, revelers mark the occasion with parades, parties, mariachi music, Mexican folk dancing and traditional foods such as tacos and mole poblano. Some of the largest festivals are held in Los Angeles, Chicago and Houston.