Yes, that's more than adequately rational of him if you subtract your mindreading that ascribes willing malevolence.

You're arguing in bad faith by assuming that the equivalency is obviously poor when he's saying flat-out it's not by making it, and not obviously in jest. If you were to make an argument as to why it's a bad equivalency, refer him to an argument that someone else has made, or give up on arguing because he's starting too far from where you're comfortable arguing, that would have all been reasonable enough.

Bu by assuming he's being disingenuous and giving a point of a sort that you would reject as fallacious if used against why trans people should identify as trans (i.e. "look how much it's gonna mess up your life"), you're just not arguing any longer. It's moved into supra-argumentative rhetoric: trying to get in good digs but without engaging particularly intimately with the logical structure.

Obviously if someone is wrong there's something amiss with their premises or logic; the point of argumentation is, largely, in pointing out where that is. The question, however, is whether the mistakes are honest or made for rhetorical flourish, and whether the other person is open to alternative ideas or just rationalizing their position irrespective of anything they could possibly learn.

Anyway, I happen to think he's more wrong than right, so I'm chiming in there. But I think it's pretty clear that you were the one who made the move from reasoned debate to rhetorical posturing.