Characters making faces
Derpy is not the only pony known for making silly faces. Characters in Friendship is Magic also tend to contract this common symptom during strange occurrences, or sometimes intentionally.
Simon says...put your hands on your nose!
"Did someone just...compare ME to Gary Oak!?"
Silly Pinkie Pie. Your not a cat
Hey Rarity, Lily just called! She wants her face back!
A Pinkie Pie duplicate in a scene edited from Too Many Pinkie Pies
for a commercial, with Fluttershy and Rarity in place of another Pinkie Pie duplicate