Goddess Kiffa did not appreciate how stubborn this guy was and she had to humiliate him as much as she wanted. That is why she opted to use her socks to humiliate him so as to make him learn that he could not continue being stubborn with her. The mistress not only had him lick and smell her socks, but she also had him lick the soles of her sneakers.
Goddess Kiffa does not like pranks. And when her friend pranked her, she had to punish him to make sure he was never tempted to do such a thing to her again. The mistress used her socks to do it and she made sure he licked and smelled them to her satisfaction. It was humiliating as it was intended to be for it to be a sufficient deterrent to him.