My Little Pony: Friendship is Magic - Season 4 Episode 12 -

An elated Pinkie Pie is planning the biggest and best "birth-iversary" party ever for Rainbow Dash, but when another party planning pony named Cheese Sandwich rides into town, plans change. Soon, everypony is so excited about Cheese Sandwich's party that they forget about Pinkie Pie, but her pride won't let her go down without an official "goof off."