My Little Pony: Friendship is Magic - Season 4 Episode 13 -

Rarity is known around Ponyville for her confidence and class, both of which are lost when Trenderhoof, the world famous travel writer and apple of Rarity's eye, comes to town. So, when Trenderhoof's attention is drawn to Applejack, Rarity does the unexpected and begins to dress and act more like Applejack than herself, which ends up in a muddy mess.