Pi.

I eat pie every week because l like pie. I don't need special occasions to eat pie, or donuts, or cake, or ice cream. It is amazing I'm not diabetic or overweight!

Additionally, 3/21 was Down Syndrome Day (3 copies of chromosome 21). Monday 3/26 is Epilepsy Awareness Day, the color is purple. And 4/1 is Autism Awareness Day (blue) or Autism Acceptance Day (gold/yellow, because Au is the chemical symbol for gold). I'm already prepared, although I'm wearing my gold on 4/2 since I'll be home on Easter, relaxing.

π day has become a mainstream thing now, and yes, we make a pie each year for it. But for true nerd cred we make 2 pies on June 28 for τ day

We are a nerdy bunch at work - 5 kinds of pie were brought for us to geek out on!

Because pie is tasty?

Pi Day is an annual celebration of the mathematical constant π . Pi Day is observed on March 14 (3/14 in the month/day format) since 3, 1, and 4 are the first three significant digits of π.[2][3] In 2009, the United States House of Representatives supported the designation of Pi Day.[4]

Made a coconut cream for pi day.

I just didn't have time to make a gluten free, Ketogenic pie. I'm thinking an almond flour crust pumpkin pie might work at some point...

It is the only day we can legitimately celebrate something irrational.

Does Pizza count? What if we work out the calories for different sized slices based on the area of the slice?

Let's bump it up a notch, why do groups eat guacamole on October 23 between the hours of 6:02 am and 6:02 pm?

3.1415...

I have the good fortune of working with a team of engineers and researchers in Silicon Valley ... we never fail to eat pie on the 14th of March, and hold a contest for best home baked recipe. This year it was a lovely Key lime that stole the show. Alas, I'm a poor baker!