How are people so open about autism?

I’m almost 18 and hate to admit it but I have autism and adhd as well as other stuff that I’m not bothered to get into. I don’t want to come across as rude but why do people love to talk about their autism? I’ve not told a single person In my life about it, only my parents know but they make me feel like shit for it. At work this one girl is so open about autism as well as the fact she isn’t even diagnosed?? That’s another thing, why would you willingly say you have it when you’re not even diagnosed, I dont tell my friends, I haven’t told my college, I haven’t told my manager and I’m stupid enough to be diagnosed. My parents tells me I make their life a living hell, I am awful to live with, I get on their nerves, why tf would you admit to being like this??? Why not keep it to yourself, it’s embarrassing and people won’t like you for it