Pinkie π baked a pink π for π day, which was yesterday.
"Pinkie π, today isn't π day anymore!" Twilight exclaimed, "π day was yesterday! You missed it because you overslept!"
"Oh noes, not π day!" Pinkie π absolutely yeeted the π she baked out the window. "Now I have to wait until next year's π day to make a Pinkie π pink π for π day!"
And so π day was completely and utterly ignored on the day it fell upon. The end. ¯\_(ツ)_/¯