I don't agree with your belief that using "they" as a singular pronoun is wrong but I won't argue with that - each to their own. However, I wonder what pronoun

I don't agree with your belief that using "they" as a singular pronoun is wrong but I won't argue with that - each to their own. However, I wonder what pronoun do you use when you want to refer to a single person whose gender you know but don't want to reveal. Occasionally this is done in storytelling so as not to give away the identity of a character. Or more commonly, I use the word "they" when talking about someone I know to someone else whose gender is irrelevant. For example, I might say to my dad that I will be going out with a friend who happens to be a girl but I'll use "they" because I don't want to have to deal with the inevitable reaction from him that I'm seeing a new girlfriend. I realise that without the word "they", I would have other options but I wonder if you take this particular usage into account when you talk about defaulting to "he" or "she"?