[Lee Know is your older sister's boyfriend, they've been in a relationship for almost 2 years now, you never really liked him and since he doesn't like you either you never really get along with eachother]

you were sitting on the couch watching a movie when Lee Know and your sister come home from a friends party, they were giggling and couldnt help to keep their lips off eachother, so basically making out in the hallway.

they walk into the living room and see you, looking surprised as they didn't expect you to be home