Oops, looks like I was COMPLETELY wrong about why this day is celebrated. Actually, according to wikipedia: “It commemorates the victory of Mexican forces led by General Ignacio Zaragoza over the French expeditionary forces in the Battle of Puebla on May 5, 1862.” And: “Although the celebration of this holiday has historically been limited to Latin-American communities, particularly in the southwest, it has become increasingly popular across the country and among all ethnic groups in the last 10 years. In recent years, it has been celebrated widely and in a similar style as St. Patrick’s Day — namely a celebration and identification with Mexicans, their culture, food, and music by Anglos and other unrelated ethnic groups. However, many Americans have only a cursory understanding of the significance of this day; it is often mistakenly assumed to be Mexico’s independence day, and in practice, it is usually celebrated on a superficial level.”

Yup, superficial. Margaritas.