Use a 2nd towel? That's what I do.

You should play contact sports such as American Football, Martial Arts or Boxing, to let all that anger out. It worked for me when I was an angry kid, it should work for you! Give it a try and sign...

Let all that waste out buddy.

The best thing to do is to sit down with him and talk about that. If you don't like it, then you should just simply say that you want him to stop doing it.