The 14th of March, we are told, is π day because that the beginning of that amazing number in decimal notation is 3.14.
I’m not sure how you celebrate π day. Dance round in circles? Go on and on (as many of us are wont to do) without ever repeating ourselves (not something I can do).
On the basis of the photos I have seen, some people bake pies for π day. If you bake a tiny pie with a one inch diameter its circumference will be π inches. Even more π-like would be to make a pie whose area is π but I am not going to try and do the maths.
Furthermore, if you cut an apple in two horizontally to make a circular section then, if you attribute the value of one apple to the diameter, the circumference will be equal to 1 apple π.