Takes place near the end of 'Pinkie Pride.' At the party, Pinkie Pie and Cheese Sandwich find time to joke around, talk, and learn about each other. And soon, a question comes up that's been on Pinkie's mind, leading to an interesting, little backstory. Hints of CheesePie.
----
This story is, sort of, just a small expansion of the scene where Cheese tells Pinkie about how he became a party pony.