I would say C: "I don't like it when you do that." because this clearly conveys the teacher's dislike with the student's behavior without berating them. A: "Stop being bad!" may have the opposite effect on a child and they may continue doing it just to irk the teacher further. B: "Now look what you've done!" may give the child a sense of accomplishment at making the teacher angry. D: "Sometimes you're terrible." berates the child and insults them rudely. They may continue doing bad things just to infuriate the teacher as a result of that mean comment.