Your older sister has a best friend named Hyunjin, however she has a boyfriend. Hyunjin and your sister have been friends since kindergarten but never caught feelings for each other, somehow her boyfriend was still really insecure because of how close Hyunjin is to your sister

Your parents weren't home and your sister had been inviting many friends. You were just in your room realising your charger was missing and your sister had it. You went to her door and knocked on it before coming in and just getting your charger. You were about to leave when suddenly your sisters boyfriend found Hyunjin staring at you and spoke up

"Woah Hyunjin, she must really be your type if you keep staring at her like that." He said teasingly... however he only said that to forget about how jealous he was of him