Ok, this is long and complex. I'll do my best to simplify.
I just got a new job in a small archive focused on a regional ethnic group (I love my job!). The archive is affiliated with a small private university which was founded by this same ethnic group in the late 1800s. I belong to this ethnic group.
The university used to also be a seminary affiliated with a specific branch of a protestant religion (Let's call them the Blue church). The seminary closed decades ago, and any religious overtones on campus are much more general now. Not everyone in my ethnic group belonged to the same branch, and in fact, there was much division between certain factions of the Blue Church, to the point where many branches split off and formed their own congregations. These branches still exist in our community today, so it's not uncommon to know other people who belong to the Azure Church, the Turquoise Church, or the Periwinkle Church, all sharing the same ethnic heritage.
Our archive focuses on collecting records and artifacts from this ethnic group, REGARDLESS of political or religious affiliation. We want to include and preserve all voices and experiences. I was raised in the Azure Church, but don't have strong ties to it anymore.
It's shocking how often patrons will ask me what my religious affiliations are! I'm uncomfortable talking about that in a professional setting, because the wrong word or impression to the wrong person could cause offense and we could lose donors. There used to be rumors passed among some groups that whenever the archive was given a donation that was related to X or Y sub group of the ethnic group, the archive staff burned it because "
those people" were "bad." It's completely NOT TRUE, but gives you an idea of some of the issues I need to be aware of to do my job well. I am ususally able to deflect and bean dip. But there is one guy who won't be distracted.
He used to work for the university years ago as a fundraiser. He also attended school here and seminary, and fancies himself to have been something of a basketball star (I only know all this because he donated a copy of his self-published autobiography to our archive). He's a pretty in-your-face person. He was a pastor in a Blue church before moving on to join an Azure Church (under some controversy of the extramarital kind). It seems he thinks that everyone who works for the university should be overtly religious, but as it doesn't affect my job, I don't think it's anyone's business.
All my dealings with him thus far have been through email. Every single one has asked in different roundabout ways what my religious status is. The email I just got from him this morning has done away with the subtleties and says,
"Have a nice Advent and Christmas. Considering your roots, are you Azure? Good to have Azure people on our staff, and students too."

It's not rude if I ignore a question that is itself pretty rude, even if it's asked directly of me, right? Anyone think I need to respond, and if so, what would you suggest?