If you are tuned into the other person; if you care about their pleasure and their personhood, you know. Grabbing someone’s ass is very different from touching them on the arm or shoulder. Patriarchal culture has taught men to persist, to not take “no” for an asnwer; to believe that she really wants you even when she (or he) says no. Women live in patriarchal culture as well. It’s all over popular culture, including movies. Yes, it would have been ideal it he had said something in the moment, and we want to move towards a society where that can actually happen more often but when you have been victimized before, as most women, and some men have, it’s not only “flight or fight” — sometimes it’s freeze…. sometimes it’s “fawn.” This is well documented. Should he continue to deal with his traumas — sure, but that doesn’t make it OK to grab his ass, particularly in a work setting. And by the way, don’t touch a pregnant woman’s belly either; just because people’s bodies are there, doesn’t grant people access to them.