Celestia likes her routine. Tax reforms, grants, laws and construction projects are all a princess needs to be content. It's just her luck that for Pinkie Pie, "content" is not nearly enough.
It can be troubling at times, when you like nice quiet evenings, and your marefriends have a much different idea of fun. But then, being out of your comfort zone is what brought you together.
Trixie and Applejack, the most and least honest ponies in all of Equestria. Two ponies who couldn't be more different and yet... they can't seem to get enough of one another.