All I can say is that for virtually all other stereotypes, from walking fast to dyed hair, I don't get it remotely. I'm like, "What are you talking about?" But sitting weird? Oh shit, this is a personally callout post now.

Yeah I relate to it too, lol. I don't think I do that all the time but I have definitely gotten some weirded-out comments before on how I sit (e.g., sitting with my feet up on a couch, for example). I have ADHD, though, and I have met many straight people who have ADHD who do the exact same thing, which is why I might think it might just be a "neurodiverse" thing and not actually relevant for LGB people who don't have ADHD, for example.

But overall, I guess I am willing to entertain the idea that many, if not most, stereotypes have a kernel of truth in them?

I hear you. That is often (but not always!) the case. Honestly, my problem is not so much with observing stereotypes as with enforcing stereotypes. Because I've seen so many LGBTQ-identified people, both online and offline, not only observe a stereotype but then assume that they should act like the stereotype in order to be "more gay"! Which makes no sense.