CERVEZA GRATIS!!!! -- FREE BEER!!!!
And the funny thing about it is... it's NOT Mexican Independence Day (that's on September 16th). Cinco de Mayo celebrates the Battle of Puebla, where the Mexicans defeated a superior French force. (It's like celebrating the Battle of Bunker Hill or Lexington and Concord).
Needless to say, like St. Patrick's Day for the Irish, it's been co-opted by advertisers as another day to throw a party. I'll drink to that (hic!)