Look, if someone grabs your ass its generally b/c you have given some signal they think its okay.
That's not to say that there aren't assholes out there who will do a random grab, but they are opportunists that are easily dealt with. If its in a public place like a bar, and there are other people around, confront them directly. Look them in the eye and say loud & firm they are NEVER to touch you again.
If its in a workplace the situation is a bit more delicate. But for the most part, it can be dealt with in a similar way: Listen, Joe, I don't know what you are used to here, but I am here to WORK. Period. If you ever touch me again, this will go to the next level. I would hate for this to affect our working relationship, so I'm going to let this incident go. But I hope I have made myself clear.
If you are firm but not a freaked out bitch, you will get an apology. He may not like you after that, but chances are he'll just avoid you.
Women harassing men is a bit more difficult. Women are often more vindictive. I don't envy CB his workplace in this regard. But he seems smart enough to tread carefully.