Since I am not a mathematician (nor portly, thank you very much), I just celebrate the pastry.
Coincidentally, today is also a Van Holiday! I wrote about this nascent holiday last month, when it fell on Valentines Day and Oregon’s Birthday. The point of Van Holiday is to celebrate your inner rock star; so I think it’s only appropriate on Pi Day to celebrate your inner math rock star. I think your geek rock star is acceptable too, if like me, you find math rock a little too esoteric.
But in any case I’ll be celebrating my Pi Day and Van Holiday by going to a 1 year old’s birthday party. W00t!