[~Misguided Ghosts~]

I don’t think it would hurt anything to tell his mother. He would likely be upset, but he shouldn’t be exposing himself to people like that without the person consenting to it first. It’s one thing to verbally ask permission to expose himself and for you to say no, but it’s entirely different to expose himself without your permission. There’s a possibility that he will continue to think it’s okay to do this to other people so it would help if someone talked to him about consent and similar matters, even if that person is his mother.