As chair of a department that I had thought I knew well, I discovered that bullying is rampant within academia, although it is often disguised as something else (including, alas, academic or intellectual freedom). I started talking about it, and very soon articles on bullying were in circulation not just within my department or faculty but across the institution.

Apologising to bullies can keep the peace but does not solve and can ultimately exacerbate a problem in the workplace. You were in the right, having asked and gained permission even for the apparent dress code violation, you obeyed your immediate superior when he ordered you to change clothes. In sharp contrast, he has violated several codes of conduct, professional and ethical and yes, Christian -something that matters, explictly, in this particular case. He has no right to say what he said to you – not any of it, at least as reported. An apology from you to him would effectively state otherwise, would grant him that right.

So go to your – and his – boss, and explain what happened. Apologise to her, perhaps, for any trouble that this might cause, since you are clearly not the kind of person who deliberately stirs up trouble for anyone (your reaction to your public dressing down confirms that) but be clear that you dressed exactly as expected and approved, and were belittled and insulted for it, and your working relationship with your immediate supervisor is thus in jeopardy. This is a workplace issue, and she is the one who, for better or for worse, needs to deal with it.

If it were up to me, I’d fire him on the spot, and hire you.