Today is an extra-special day for Discord. One he's been looking forward to all year. Or rather all day, since he had just learned about it previously from Fluttershy. A day that's all about him, all about his needs, his greatness, and how truly awesome he is. A day to feed his ego like the gluttonous pig it is.
Why, it's Discord's birthday of course!
What, you thought it was another type of celebration day? Please, don't be a fool.