Okay, let's be real here. High school is judgmental as hell. Everyone is in a clique. I was in a clique, you were/are in a clique, even that one kid that says he isn't in a clique since he doesn't hang around with anyone is in a clique because he's in a clique by himself. When I was a freshman and sophomore in high school I thought I was so lame. I didn't do sports (or any club, for that matter), I didn't dress like the other girls, anything. I didn't have many friends. I had acquaintances, sure. But I remember constantly panicking over not having a partner in class, who to sit with at lunch, etc. I remember trying so hard to be "cool" in the beginning. I tried to dress like how I thought all the other "cool" girls dressed, I joined the basketball team (and broke my collarbone in practice, which resulted in me quitting), but I just wasn't comfortable. I wasn't "cool", I was pretty lame. I wasn't going to fit in with all the "cool" people no matter how much I tried. And eventually, I stopped trying and accepted it.
When I was a junior, I remember sitting in study hall with a few of my many acquaintances and us thinking the people who sat at the table across the room were so annoying. They always laughed too loud, caused a ruckus, and played weird games about wizardry and mythical creatures (I actually have no idea what they played, I'm just assuming it was something along those lines). I was always glaring at them with the internal thought that my hard stare would shut them up. Until one day I was introduced by a mutual friend to a guy who sat at that table. I recognized him. He was in my gym class and was always alone because he had no friends in the class. After talking to him, I realized we liked a lot of the same music, and I decided he wasn't half bad. A couple days later in gym I saw he was alone and decided to go out on a limb and ask if he wanted to be my partner. By the end of the class, I found out he was actually really funny and my first impression of him went down the drain. He was my partner for the rest of the semester and 3 years later he's now one of my best friends.
After quickly becoming friends with him, I decided to leave my table of acquaintances and join him at his annoying study hall table. And after a few days, I found myself laughing too loud, causing a ruckus, and even though I didn't play their weird games, I decided not to judge anymore because it was way too complex for me to even figure out. All the people at that table were so incredibly nice and entertaining I was mad at myself for having such a judgmental impression on them at the start. I remember being so sad everyday when study hall was over and I think back on it now as probably one of the more entertaining classes I was in.
For the rest of junior and senior year, I decided to stop being so quick at giving people first impressions. I remember there was a "goth girl" that everyone found a little weird, but I thought she was an amazing artist and I applauded her for being the only person in my entire school (I went to an extremely small school) that stood out from everyone else. There was a girl in my class who was bullied into being homeschooled because everyone thought she was weird, but I always thought she was one of the funniest people. I was so glad when she came back my senior year and started actively participating in class and everyone could see how funny she actually was. And whenever I see her, I always think to myself, "There will never be another person like her." In gym class senior year, it was pajama day at school and I decided to sport a nice black and pink onesie, and a boy who I always found a little dorky was instructed to stand by me and sheepishly turned to me and said "This might be a little weird, but you look adorable in a onesie." And I still remember it to this day because it's probably one of my favorite compliments I've ever received. I found out that most of the "unpopular" kids were actually some of the best and most decent human beings in that school.
Long story short, don't judge someone or give them a bad first impression. Get to actually know them. Have an open mind about them. You never know... They may surprise you, make you think differently, or even end up being one of your best friends.