I'll bite, even though I'm comfident you'll do exactly what JB said you'd do.

It was offensive because like eveything to do with the trans delusion/movement it makes a mockery of women. It pretends, and then tries to force sane rational humans into agreement, that men can just decide to become women, and poof it's so. That the whole idea that we can somehow seperate our selves into physical and spiritual/metaphysical (use whatever term you want) beings where it is possible for us to use the recent idea of gender as distinct from sex and therefor self identify as something we are not. Until 5 minutes ago this would have been wholesale laughed at (rightfully so) and yet today people take that feces seriously. It was double offensive to many because the dude was not only pretending to be female, he was playing the role (and still is from all evidence) of a 10 to 12 year old female. I am aware that there are some serious mental health issues that go along with the very rare issue of gender disphoria, but for the most part the recent contagion of "trans" is attention whoring and grown-ups failing to be grown-ups.