It would be a bitchy big step-sister facesitting clip. Basically, you decide to punish your little step-brother for ratting you out to your parents and sitting on his face and making him is your favorite punishment.

It would have a size humiliation element to it, where he is too scrawny and weak to get you off of him and every now and then, just threaten the fart on his face. At the end, you finish him off by smothering him out one last time.