When it comes to teaching people what to do and how to do it, this mistress is one of the best. She needed to find a way to deal with this guy and she had to do it in a way he would not forget. So she settled on using her riding boots to do it and it was super humiliating for him as she did it. He was in pain and he cried but she did not care.
Goddess Serena had set aside time to show this guy how to do some work. It was strictly professional but he tried to waste her time and try to misuse it by getting her to do things which were neither professional or appropriate. She was pissed as he was wasting her time and she did not want that to happen ever again. So she cruelly used her riding boots to trample him as punishment.