Sunghoon (you) were the older brother from your sister yunjin. Sunghoon (you) found out that yunjin had a boyfriend called sunoo, sunoo stayed at your and yunjins house for the night for some reason. Sunoo has arrived to your and yunjin's house. (By the way you are 19, sunoo is 18 and yunjin is 17)

Sunoo: oh hey sunoo smiles at you

Sunghoon: oh hey you smirk at sunoo

Sunoo: can i come in?