X and I hadn't seen each other since we were in grad school together. We were standing around with a couple of graduate students during a conference break. Y came bounding up to us, stuck out his hand to X, and gave him an unusually vigorous and ostentatious handshake. Y had been a grad student with us at Princeton, a few years ahead of X and me, and Y knew the two of us equally well.
Reflexively, I stuck out my hand to shake Y's. He looked at my hand, and then put his hands behind his back. It felt, metaphorically, like a slap in the face. The grad students watched the scene unfold, and I felt embarrassed. Eventually it dawned on me that Y's refusal to shake my hand was based on religious grounds.
The affiliation that he had written on his name tag was a U.S. government intelligence agency. So in some sense he was there as a representative of the U.S. government, and his trip was funded by me and other taxpayers.
When I saw Y at a conference break the next day, I pointed out that while I understood, respected, and supported our country's strong commitment to freedom of religion, as a taxpayer I had a reasonable expectation that he behave professionally and fairly in professional settings in which he represented my country. As such, I felt that if he would not shake the hand of a female colleague for religious reasons, he shouldn't shake the hand of a male colleague in a similar professional setting, as a matter of basic fairness and common decency.I asked what message was being sent to the two (female) grad students who had witnessed his handshake the previous day, about the differences in the way female and male mathematicians are treated by their colleagues and by people representing their government.
He agreed with everything I said, and even agreed that not shaking hands with men in professional settings was a fair and reasonable solution.
We discussed other ways in which he treated his female and male colleagues differently on religious grounds. One example he gave was, if someone were noisily vacuuming the hallway outside his office, he might close his office door when talking with a male colleague, but not with a female one. I pointed out that such actions could give an unfair advantage to one group over another, and suggested that he follow the same protocol as for handshakes: in professional settings, if he wouldn't do it with a female colleague, don't do it with a male colleague.
He explained that the prohibitions he followed were designed to get the practitioner not to think about sex. (And by putting his hands behind his back in response to my outstretched hand, he was reminding himself not to think about sex.)
After we discussed this point for several minutes, I remarked that this conversation was one of the few times I had talked about sex in a professional setting, and wasn't it interesting that his religious practice seemed to lead him to talk with female colleagues about sex, rather than preventing it. He agreed that it was interesting. (I could have pointed out that there are things I would rather discuss with my colleagues than sex or gender. And that I was surprised by how much he seemed to enjoy talking with me about thinking about sex.)
I don't know whether he now treats people equally and fairly in professional settings, irrespective of (his perception of) their gender. But I'm glad we went through the intellectual exercise of discussing it. I hope it gave him more to think about than sex!