Jean was unsure how long the joke had been going on for, but it was getting a bit annoying. He was not even sure how it started. When Jean looked in the mirror he didn't see a horse, but I guess everyone else did.
After the millionth horse face joke, Jean decided it was time to get everyone back for everything they had said to him. After a lot of bargaining and laughing, Jean had the perfect idea and just the props he needed.
The next day while Jean was feeding the horses, Eren, Armin, his beloved Mikasa and everyone else from 104 had ran over yelling lame jokes. Everything seemed normal until Jean didn't turn around to yell at them to shut their traps. Eren had placed his hand on Jean's shoulder, shaking him, slightly. Jean then turned around and to Eren's surprise he literally had a horse face. Eren jumped back and started to scream (and maybe cry).
"What is it Eren?" Jean asked as he walked closer to Eren. "Is there a problem with my face?" He continued. Eren just gaped at Jean and Armin was trying to pull Eren away, but Eren just sat on the floor staring at Jean.
Jean was inches away from Eren's face when he pulled off the horse head that he had gotten from Hanji, who 'had been waiting for this moment'. "DON'T EVER MAKE FUN OF MY FACE AGAIN JEAGER!"