This slave thought he was macho and he could avoid being used the way he thought other slaves were being used. So she went ahead and she used her boots to trample him and also forced him to lick the dirty soles. That was to show him that he did not have any powers and that he was nothing to her. He realized that and he started acting the way it was expected of him.
When this guy was rude to these mistresses, he thought nothing would happen to him the way nothing had ever happened to him the other times. The mistresses knew his kind and they used their knowledge to lure him to their house and when they got him there, he was turned into a boot licker and forced to lick their dirty soles. He was told that if he did not, he would be crushed on his nuts.