Mistress BlackDiamoond is good at nipple torture and she wanted her friends to be too. That is because it is an effective means of punishing and teaching a lesson and could be applied in any scenario. So she had it used the way she wanted and the mistresses had a great time teasing the loser, torturing him and learning from their friend. The guy they practiced on was paid for his troubles as he had done nothing to warrant the punishment and torture he got.
Mistress Kasha and mistress Van Licks wanted to dominate this guy in order to get info since he had refused to give them the info that they wanted. So the mistresses went out of their way to teach him a lesson they were sure he would not forget. The mistresses laughed at the guy as he peed his pants while begging them to forgive him and to stop torturing him. He gave them the info.