Ok, so here's the deal.
Not unlike the American revolutionaries and the Britts, Mexicans were having problems with the Spaniards.
In an event similar to the Boston Tea Party (no taxation without represntation), the Mexicans refused to pay the taxes on a ship load of mayonaise. Following the lead of their neighbors to the north they dressed up like a bunch of Indians (that took about 30 seconds) and sunk the boat, mayonaise and all. It was on May 5th. Cinco De Mayo