Final answer:
Harper used direct intervention as a bystander, by confronting the individual who made a sexual assault joke, thus demonstrating prosocial behavior and challenging their actions directly.
Step-by-step explanation:
Harper used a form of bystander intervention known as a direct intervention. This approach involves addressing the situation head-on by confronting the individual who made the inappropriate joke. Harper's response to ask for clarification with a serious face and then to comment on the friend's better self represents a direct challenge to the friend's behavior, aiming to make them reflect on their actions and potentially prevent such behavior in the future.
In contrast to diffusion of responsibility, where people are less likely to intervene because they assume that someone else will take action, Harper's direct intervention is a demonstration of prosocial behavior, which is action intended to benefit others. This type of intervention is crucial in promoting a safer and more respectful community by not ignoring inappropriate or harmful behaviors.