Mistress Vivian flirted with this guy because he looked like the total package. He was handsome, he was well built, he smelled nice and he dressed nice. She thought that he would be courteous but he turned out to be a jerk. She was so pissed at him that she forced him to eat her shit. The guy was degraded but he knew that he had no choice other than to do what she asked him to do.
Mistress Vivian had no time for any illogical person in her team. She had tried to look the other way a few times but she realized that things were not going to improve and so she had to do what she had to do. That is why she chose to shit on him to make him realize that he had to change. And indeed he did after that cruel humiliation.