I have written quite many blog posts about this particular subject, but here's a summary if you haven't read them: Matt Parker is a very popular math popularizer on YouTube (with over 1.2 million subscribers, which makes him one of the biggest if not the biggest youtuber of this kind). I have been following his channel for quite a long time (over ten years now) and have always been a big fan. It became quite a pet peeve of mine, however, when some time in the latter half of 2019 Matt started some kind of personal campaign of trying to make the "they" pronoun the universal "gender-neutral" third-person singular pronoun. I indeed checked when this change happened, and it was around that time: Prior to late 2019 he pretty much never used "they" to refer to a single person, and there are countless examples of him using "he" and "she" without any problems. Then, some time in late 2019 not only did he suddenly and completely change th...