Only puts in one earbud (whether because the other one is ALWAYS broken or because they want to be able to listen to music and everything around)
Never has acne, but has enough other skin problems to make up for it
Allergic to mint, which causes rashes on their face (I have this and it sucks)
Always turns their screen brightness and volume down as low as they can (or direct opposite)
Always wears certain jewelry (rings, earrings, bracelets, necklaces, toe rings)
Never listens to "normal" music. Only musicals. Or not music at all. Only podcasts
Can't read because they always have a song stuck in their head
They go through insane phases of hyper fixations where they constantly make references to something but never go on tangents
Never cleans their glasses (or direct opposite; always cleans them)
Tries to dress nice but has no fashion sense
One last thing. Giving your most likable character glasses isn't a bad idea because some people (cough, cough, me) hate their glasses until a character they like wears glasses, then they love their glasses. It can really make an impact! Just an idea. (That sentence made no sense, sorry)