Reminder: MC (so you/your character) is whatever gender!
Nail polish is something for your nails, everyone has nails, and so it is for anyone who wishes to wear it.
Daniel:
He already knows how people will comment on it, but people always seem to find something wrong about him to comment about so might as well do it, especially as you want to do it. It's a nice bonding moment with you.
Zack:
Fuck no! He can't do that. Everyone would mock hi- but wait... It's you. With your gorgeous eyes, wonderful personality, those lips he can get kisses fro- Okay may do it, if he gets a kiss as reward. Afterwards if anyone comments on it he is quick to start yelling with a reddening face.
Jay:
He actually likes it but is too embarrassed to do it himself so now has an excuse to wear it. He matches his outfits to it well. If anyone comments on it he gets bashful but proud he can now reveal who did it.
Vasco:
It gets him feeling excited and giddy. Best to go with colorful stuff and patterns. He wears it with pride! When Burn Knuckles awkwardly comments on it, as now their leader is wearing nail polish, he doesn't give a single fuck. His fingers look fun!
Jace:
He gets embarrassed, nervously laughing 'no way' as then every guy would mock him and his reputation would fall. At the same time he could brag that his partner did it for him... So, with a sigh, he lets you do it then mostly has his hands in his pockets afterwards.
Johan:
Sure, go ahead, just no silly colors or patterns. Usually just neutral colors for him. He will keep it on, he doesn't care. Anyone have an issue with it? Their next worry won't be his nails but their broken nose. His comment after it is usually "Shut up, my partner did their best to apply it". For him it wasn't an insult to him but an insult to you.
Jake:
Do anything you want to him! But if you do his nails then only fair he would be allowed to do yours. Once done he makes you promise not to take it off, so both keep it on no matter what each other did to the other's nails so can go as serious or goofy you want with it.
Gun:
Only black is allowed, or white if he's feeling fancy and has white clothes planned. He doesn't care if his nails are polished or not. During it he will keep annoying you by grabbing your hand, pushing it, tickling your palm until you complain, then he is smug as he is victorious in having annoyed you.
Goo:
Yees! He loves some nail polish. His fingers look great with it and he will show it off to all his opponents before he fights them. A playful shake of his fingers, "You like~?" If the person dares say no his drops and his eyes lose that playfulness. "Is that so?" is all he asks before he suddenly dashes to them.
Taesoo:
He has a good laugh each time you propose it. At first he didn't do it, as he had the mentality of 'what the fuck are you on about? I'm a man, men don't wear it' but overtime he began debating it and now he lets you do it. And damn do his fingers look pretty with some polish on it. So now he is a supporter of people, no matter who, wearing it and will beat up people who mock others for it.
Jichang:
Suprisingly he lets you, but then you realize why as you have to remove it if he is gonna leave. He lets you practice on his nails but he won't be wearing it outside, especially since it is the countryside so he doesn't need the old people stirring up weird rumors.
Seongji:
Sure, go ahead, he doesn't really care. Not much in his day to do besides the daily stuff so to sit down with you and get his nails taken care of is a nice change. Make it colorful and he will chuckle, a bit bashful and asking if this is appropriate for a man. To which you'll answer that times are changing and only one who would dare mock it is Vin Jin.