Many folks in the US don't know that Mexicans like mayonnaise. It's true, the rich, creamy condiment was revered in Mexico in the early 1900s, but because it was perishable, it was hard to obtain.
Then, along came refrigeration. By the early 1900s, refrigeration ships were regularly plying the oceans, and a consortium of Mexican grocers put together a large order of mayonnaise to be delivered to Veracruz. Unfortunately, the ship became engulfed in an off-shore storm, foundered and sank, with the loss of all hands, and the mayonnaise. The news reached Mexico on May 5th of that year,
And that's why Mexico remembers Sinko de Mayo on May 5th.
Okay, people, it's a joke. Get over it.