No, I disagree on the latter. Fifteen year olds can understand that mocking someone for something they can't control and are sore about is a cruel thing to do. There are reasons such mockery is a staple of high school bullying. Which of course does not make being hit with a rock an appropriate response, but I think that was mean of Kim, and that Bob is being worse with the stuff about Adele having violence in her "blood" (quite likely in part because LW's intransingence isn't helping).