Only one that I know of. An old sort-of-friend, who I wasn't too close with but who always seemed to crop up at parties in our social circle, came out as using "she/her" pronouns the other day. In some ways he's exactly the sort of guy you might expect to troon out. Very nerdy, probably undiagnosed autistic, has emotional problems, was bullied, PC gamer, anime watcher, MTG player, all the usual business. But on the other hand I never really expected it. He doesn't look or present as female AT ALL.
But now, looking back, I see the signs. I remembered a time way back in 2015 we were out for drinks with him and he said something about how he "used to want to be a girl when he was younger", and everyone laughed at him and thought he was joking. And he's been growing his hair out stupidly long for the past year. Absolutely cannot take him seriously in any way, still. The idea of looking at this guy and saying "she" would be absurd. Really putting the "clown" in clown world.
I don't know how I would handle it if more people I knew trooned out. The one guy is weird enough. If several more went down the Looney Troon path I might lose my mind from the absurdity of it all. Meeting trans people when they're already trans is fine because, as ridiculous as they often are, you go into the encounter knowing of said ridiculousness and knowing that they're not playing by the normal gender rules. But seeing someone who you always knew as male/female, who always presented as that gender, who never openly vocalised any gender confusion, suddenly turn around and say "hey I'm trans" is mind-boggling. Calling someone "she" who you have always known as nothing but he, or vice-versa, just feels very tangibly wrong on some level.
By "wrong" I don't even mean that it's degenerate, but that it simply feels like a warping of reality. It feels like they're cosplaying as the other gender but somehow insisting that it's actually real. And, when other friends are corroborating that and agreeing that "yep they're a girl now", you get that sinking feeling like you're not in the same reality you thought you were a few short years ago.
