I agree with being careful about the legalities of a physical confrontation. I spent 10 yrs in prison. My experience is don't get caught period, as soon as you say you told authority about the problem. They will say you planned to do wrong and that will make you liable. Some problems or rather problematic people don't understand anything else other than physical violence. This person thinks because you are overweight you are sub human and therefore don't deserve the respect others do. I myself have always been overweight and had similar struggles when I was in school. If you are certain that teachers exec. aren't going to do anything then what good would saying anything do. Other than alert them to the fact that if your pest shows up injured they will know who most likely did it. Remember this type of person is weak and wont be able to take to much. Only use as much force as is needed to get his attention. So control your emotions. I don't believe that you don't care as long as people stop. I think it bothers you every time it happens. So don't let all that hurt, hurt your pest. Because you might end up feeling bad for the damage you did. For self respect and to show enough is enough. I'm sure a black eye will do the trick. But don't let anyone see it happen and deny it when accused. I know that doesn't sound great, but something like this can turn out bad either way. Be Careful with your anger it can cost you more than you are prepared to pay. Restrooms are pretty private. O and don't brag just handle business and move on.