Mistress Xue wanted to dominate this guy and she knew that for it to be the kind of lesson he needed to learn, she had to make sure that he learned it the hard way. That is why the mistress opted to vomit on him and make it so gross that he would not forget it in a hurry. And that is exactly what happened to the guy. He never forgot it.
This guy was rude on goddess Yi for no reason and she was not going to accept that from him. And so she gagged herself and she puked on him after she had tricked him into thinking that she was interested in doing some naughty things with him in order to have him follow her to his punishment site. He checked his rudeness as he did not want to experience that again.