I'm a 38-year old 아줌마 who also got into K-Pop recently-ish (right before BTS became, like, the biggest thing EVER). There are definitely people who raise eyebrows or giggle when I tell them how much I love K-Pop (Why would I be stanning a bunch of teenage girls?) If people question why I like it, my typical response is "Because it's fun and it makes me happy and there's enough stuff in the world for me to be sad about." I also started learning basic Korean and everyone always looks really stunned and impressed when I bust out an 안녕 (I always think "BOOM Y'ALL, CULTURE!)
But I'm an adult and I understand that school is a different world. I was picked on all the time in school, and adults being all "Just ignore it!" or "You shouldn't let words hurt you!" was NOT helpful. But slowly I learned that being the same as everyone else was really boring and that the stuff I liked was cool and that my actual friends may not get it, and may even think it's silly, but they love that I love it and that it makes me happy.
I wouldn't tell too many people at first, but my family and best friend knew I listened to kpop, but once I decided it wasn't that big of a deal and was more open, I found so many friends through kpop, who became my concert buddies and people I could discuss new comebacks and major news/scandals with lol. Maybe because it's more acceptable where I live, in California, but honestly I would recommend not hiding something so trivial. I guess since you're still in high school, you could be more sensitive to what other people might think about you, but trust me when you get a little older, you won't care anymore.
People don't know a lot about K-pop, so it seems like I like something completely inexistent. I'm 38, and since I started listening to K-pop, I stopped listening to everything else. Cardi B, Ariana Grande, you name it: I don't listen to that kind of music anymore and I don't even know many of the artists that are "hot" these days. I don't mean to be rude, I'm just interested in K-pop and everything else became secondary or invisible (in terms of music). I've said that I like K-pop a few times, but people don't care about it if it's not on the news all the time. I've heard "you like the fat guy from Gangnam Style?"; and that would be the only thing they know. Obviously, if they see anything about BTS "oh, you like these weirdos, they look like girls"; actually, BTS is not my cup of tea. So people start staring at you because that's where their knowledge of K-pop finishes: "what do you like then, are there more groups??". My ex boss saw a picture of Stellar as my phone wallpaper, and she looked at me like "wtf is this". I've been to a few K-pop conventions (I love them) and my mother has told me "you're too old for that, there are kids in those places". I love K-pop and I wouldn't change a thing.
Btw, my boyfriend doesn't like K-pop, but he likes Super Junior's version of the Luis Miguel song and he helps me making mashups with K-pop and songs that are not from the same genre (like BVNDIT and Red Hot Chili Peppers. I'm working on it.)
If you want to show off the things you love but feel nervous, start small. Put a photo card in your phone case, stickers on your notebooks, pins and keychains on your bags. (I carry a backpack to work and right now it looks like a walking IZONE/Everglow billboard.) Share music with your friends, or play songs out loud. When I turn on Spotify at work, inevitably someone will wander over to me and say "Hey, what are you listening to? I like the beat/sound/voices/everything." It starts a conversation.
The one time I had someone flat out tell me being a K-Pop fan was dumb and the music was bad, I very sweetly replied, "Then it's so good you don't ever have to listen to it!" They were so shocked that sarcasm-ed them back they just sort of looked and me and then walked away.
Love what you love. It is SO OKAY to do that. Everybody's got their something, and it's part of what makes you YOU. And it's okay if you feel embarrassed or uncomfortable telling people, too. Not everyone is entitled to know your business, nor are they entitled to an explanation about why you're into the things you're into. (I didn't figure that out until way later in life, but I hope that maybe you can keep it in the back of your mind.)