Mistress Marla did not want to deal with her ex again. He had been a pain in the butt for her and she was done with him. Trying to deal with him again was a headache in itself and she had no capacity to stomach such nonsense. So she cruelly crushed his balls so as to teach him a lesson and make him learn never to try looking for her again.
Mistress Marla does not like to be conned and when this guy did it, he had to be punished. The mistress chose to ball crush him as punishment and she did not care what he felt as she knew he deserved it. He was a con and the mistress made sure that he would not con anyone else after her. And that was why she crushed his nuts like never before.