Because if you did realize it was the day to celebrate the traditional Mexican dish of a flour or corn tortilla packed with stuff (i.e. Taco Bell's entire menu), you'd be too busy eating to be reading this. What, you can read and eat at the same time? What are you, some sort of hideous mutant?
I've been celebrating by playing Zynga's Rubber Taco on Facebook, a game about a family of bouncing luchadores attempting to recover their stolen food.
As for my food, I just sent my wife out to Moe's (WELCOME TO MOES), which isn't exactly traditional but it's close enough that I don't have to wait too long for crunchy, meaty goodness.
Plus they have pork, which reminds me of Deadpool's face, and since he's the one that reminded me about National Taco Day, I think that's incredibly appropriate.
So stuff your face, and don't worry about guilt—it's also National Vodka Day!