This is a hard one. Especially because I'm in my 30s and a completely different person (of course, but sometimes we need to remind people we are all individuals when commenting online).
I don't really talk about BTS or any of my hobbies with others in the real world, not that I'm a particularly private person, but the hobbies are for me, I don't need to share them. I have searched out online communities to share with, because it's always nice to talk to people that like the same thing.
I do get a hard time from my husband, and unfortunately he picked on me in front of his family, so now they all think it's okay to have a go. Like you said, it's for no reason, none of them have listened to BTS, I don't talk about BTS, they just bring it up to have at me.
I used to argue with him, not to defend BTS, he is entitled to his opinions, but to defend myself. It is never okay to pick on people for having hobbies or likes that you don't share. Which is what I said to him, when he realised I felt like he was attacking me, he tried to stop. Some people just make those off hand comments. They don't think, they are not trying to be malicious, they are just thoughtless people.
I know you're not asking for advice, but I do want to say, never feel like you have to defend BTS. You do not. Their success speaks for itself. But do defend yourself. If they are family or friends then you can tell them that their words may be intended for BTS, but really their words just belittle you and a hobby you enjoy. If it's a stranger, depending on how liberal you are willing to be, a variation of "get your own life and leave me to mine" could be acceptable.
But all that said, my husband will still make remarks, even though he knows how it makes me feel. He does it without even thinking. If I have head phones on its "listening to that garbage again" or if I'm on Reddit "are they really worth reading about". Now I can just call him out and he apologises, but I'm mentioning it because it can take more then one talk to get the message through to people.