I'm lucky with one of my interests - human anatomy - as I work in a pathology lab, so nobody thinks it's at all weird. People outside vary; some find it fascinating, some think it's a bit icky, and some will ask me questions which, not being a doctor, I'm not qualified to answer. So I tend to keep quiet elsewhere.
I pretty soon learned at school that opening up about my afterlife/death/occult type interests often either got me seen as morbid, or targeted by religious freaks wanting to tell me I was in league with Satan. So, same goes for that one.
And, the Kurt thing varies. Most people know I'm a Nirvana fan, but a lot of people don't realise how much. (Many have not, for example, seen the tattoos ....) There's the 'You're a bit old for that, aren't you?' reaction, and then there are the other reactions which teens who are into him sometimes get which are the 'OMG you must be into drugs/about to kill yourself' reactions...and then, even in fandom, there's the conspiracy theory stuff, which I have no interest in. So, again, tend to keep that one to myself.
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"Grunge? Isn't that some gross shade of greenish orange?"