Goddess Nika does not like people who bend the truth and misrepresent facts. This guy was one of them and she did not want to let it be a thing where he felt comfortable doing that to her and with her. So she had to cruelly teach him a lesson and she did it with her boots. It was brutal and it was painful as she kicked and trampled him but he learned his lesson and stopped that behavior.
Goddess Nika passed her threat in a non-threatening manner. She flaunted her ass as she showed off her boots. And she told her slave that she would use both her boots and her ass to torture him if he did not toe the line and do what she wanted him to do. He was scared because he could see she meant what she said and that is how he changed.