The Trifecta of Mansplainers
There are several flaws in this story. First, he snapped his fingers in front of her face to get her attention (rude). In spite of his convictions about the woman’s posture, he started instructing her on proper boxing stance.
In order to prove that he was not going to give in, he asked her to hold on to his buttocks. The icing on the sexist cake is this.