How to solve an issue where I'm sorta just harassed at work?

So I'm a pretty large guy (read fat) which essentially means I got big moobs. I don't want to go into much detail but essentially, I have colleagues who tend to just grab my moobs and it's really starting to tick me off. At first, which was years ago, I was fine and just ignored and laughed along side (I know I shouldn't have, never made the wisest choice, I'm a *******). Theses days tho I'm getting annoying and want to put a stop to it. It's insulting, demeaning and I might just end up swinging to the jaw (I'm not even a fighter but a definite wuss but I'm getting ticked).
Problem is I don't want to be direct about it cuz it won't play out normally where people will just stop. I don't how to go about it but I'd like to make sure there's an end to this.
One thing I can think of right now is just saying "Don't touch me" in a serious tone and that's it but not sure what to do after if it gets ignored.
Or am I just overreacting? They are just laughing about at the time and they're generally just friendly people.
Edit: talking to management or HR or anything won't work. I'll turn into a joke and it'll be spun in a way that I can't take a joke etc.


Source.