Hi there, SinCity, and welcome to Psych Central. This is a tricky situation, and I don't blame you for being at wit's end.

Because your wife has already spoken to her sister about this, it would be no surprise if she learned it has continued, right? I'm not sure that you need to fill in your wife about the details of what happened, but I think letting her know that you are uncomfortable with her sister's touchy-feely behavior seems okay. I do want to hear what other's say.

The other thing is -- and bear in mind that I am a female -- is that NO ONE -- absolutely NO ONE touches me if I say stop.

I've had occasion to slap two men on the face in my life (when I was still young and cute), both times because they were unable to hear the word NO, and I had to do something to bring them to their senses. I did not slug them on the jaw, mind you, just a brisk slap. Both times, they said -- If you ever do that again, I will hit back. But they never violated my boundaries again.

I don't think you should hit your sister-in-law; unfortunately, slapping is still a gender-bound activity, for the most part. But I would make my position known in no uncertain terms.

"If you ever touch me inappropriately again, I will tell (your wife's name), and I will insist that you immediately leave our home."

Or, if you are comfortable threatening violence (even if you do not intend to follow through), "If you ever touch me inappropriately again, I will slap you."

If anyone comes back at me with, "I was only kidding around," I just say things like, "It's not funny. Don't do it again. Ever."

Sometimes, my withering look is strong enough to make people and dogs stop in their tracks. I have a strong personality and a strong voice. I know who I am, and I do not put up with this kind of stuff. If other people don't like my boundaries, too bad for them.