15 year old student touching himself in English class

This is not click bait and I'm not a bot. I teach English communication at a junior high in Japan. I work with the NET program in Osaka. I've been teaching at this school for seven years now. At the beginning of this year, I noticed one of the students touching himself in class. It was over his clothes. I'd never noticed it before. I believe he was doing it, but was doing it more stealthily, under the table and with his head down. The reason I noticed him this year, is he had his face up and his arm was moving. It made me feel violated, honestly. I was shocked. I went to the homeroom teacher afterwards and hesitantly approached her about it. She dismissed it saying that he had ADHD. My brother also has ADHD; I know it is difficult to drown out all the noise, so in a sense I can understand her reasoning. However, this student is going to be in high school next year. His way of dealing with stress is wildly inappropriate. Since then, I can't help but notice him doing it during every class. I assume he does it in all of his classes. He does it, I feel, so cavalierly. He'll do it during group activities while his table is facing others. He's done it so vigorously that his chair has been bumping into other's chairs. When I'm teaching him, I cannot look his way because seeing him makes me incredibly uncomfortable. It makes me angry that this is just looked over, brushed aside as if this is a method to deal with his ADHD. I view it as sexual harassment to some degree. I'm sure other students have seen him doing it. It's completely inappropriate. I feel like I'm walking a very, very fine line here. If I make a big deal about it, it could come off as me being inappropriate. For those of you who live in Japan, you know that people have to be careful about rocking the boat. Have any of you had experience with something like this? How did you handle the situation diplomatically? I feel that this students parents and teachers have failed him to some degree. I know it's an uncomfortable topic, but showing him a better way to release stress would have been a much more positive thing to do. For those of you who read to the end, thank you for taking the time to listen.

by vape_sensation