I find if you just use the persons name or the pronoun “they”, you can’t go far wrong. I’ve slipped up before, nobody has seemed to take offence to honest mistakes.
RuPaul is amusing on this: "You can call me he. You can call me she. You can call me Regis and Kathie Lee; I don't care! Just as long as you call me."
Sadly the notion of asking the question "How can I make you feel comfortable today?" is anathema to some. I have had to work particularly hard to avoid (getting sacked by) offending people through my lack of conventional empathy, but that's one of the downsides of being 'on the spectrum'. There is certainly no excuse for actively pursuing the prejudiced dick head's agenda.