Réponse : Dear (your friend's name),

I am writing this letter to you to tell you how I am feeling these days. I don't know if you've realized, but you are a bully. You are harming people's emotional state. You treat them badly and you expect girls and boys to respect you? The boy you recently bullied was crying and told me that he doesn't want to come to school anymore. Please, apologize to the people that you've bullied. Do not be a troublemaker, go and be friendly to pupils.I hope you'll change your mind and help those people.

Best wishes, (your name)