5 de Mayo
It seems to me that most Mexicans celebrate 5 de Mayo by telling everyone else that no one in Mexico celebrates 5 de Mayo because it is not the anniversary of Mexico's Independence. Everyone else celebrates 5 de Mayo by drinking beer and eating Mexican food (or food that resembles it). And I have never heard a single non-Mexican person say that 5 de Mayo marks Mexico's Independence.
So, fellow Mexicans, isn't it time to shut up and join the party?