It's wrong to treat a sibling's friend badly.
John is at home while he is day off and his sister, Mary, is playing with her friend in their home.
John wants to watch his favorite movie.
John goes to his bedroom and watches the movie in a laptop.
John asks Mary's friend to leave their home so that he can enjoy his movie quietly.
Mary thanks John for being considerate and agrees to stay quiet as far as possible.
Mary feels disrespected and started arguing with John.