At a government training, I once had a harassment trainer explain it very similarly. If you would not say it to your grandmother, mother, sister or daughter, do not say it. If you would not want someone saying, sharing explicit details or even joking about personal relations with your grandmother, mother, sister or daughter the same thing that you are saying about a coworker or even a stranger then do not say it. It is not appropriate. It is illegal and it will have a profound and negative impact on your career.

> At a government training, I once had a harassment trainer explain it very similarly. If you would not say it to your grandmother, mother, sister or daughter, do not say it

And this is the crux of the problem. Let's pretend that I do not have any issue having this kind of a discussion ( in passing, as a single comment or even at length ) with grandmother, mother, sister or daughter?