In early 1912, Mexico was suffering from a sever mayonnaise shortage. As it was a staple ingredient in almost all their dishes, they were nearing panic due to the lack of mayonnaise.
President Francisco Madero was able to locate 500 tons of mayonnaise in England, costing just pennies on the peso. He arranged for it to be loaded on the HMS Titanic for a scheduled to delivery on the fifth of May.
Unfortunately, The HMS Titanic struck an iceberg on the 14th of April, sending all 500 tons of mayonnaise to the bottom of the Atlantic.
This completely depressed the Mexican populace since they would have no mayonnaise. However, in true Mexican fashion, they created a holiday to mourn this national catastrophe, which they still celebrate to this day.
They call it "Sinko de Mayo".
And now you know the rest of the story.
(Happy Cinco de Mayo, folks)