It's Cinco de Mayo. When we lived in Miami, it was a big party day, as it is in every Mexican restaurant in the country. OK, it's a big holiday in Mexico, and has become a big one in this country as well, largely thanks to our huge Latino population. It seems to get bigger every year: what's not to like about eating, drinking, singing and dancing, after all.
I had it in my mind that it was Mexican Independence Day, but it's not (that falls on September 16, which tends to go by unnoticed).
On May fifth, 1862, Mexico defeated the French at the Battle of Puebla, throwing off the yoke of foreign occupation.