1. Bum has a thing for biting Sangwoo
2. Sangwoo likes risky behaviour (being a exhibitionist, speeding, agitating random people especially other men, etc). I think it might have to do with him always trying to be nice and normal around people, and sometimes he lets out a little bit of his psychotic and messy side, either deliberately or unintentionally.
3. Sangwoo always wins, at least for now. He won rock-paper-scissors with Jieun, that boxing game with jerk Yoonjae and now he has “defeated” Seungbae.
4. Sangwoo has a thing for kissing Bum after putting stuff in his mouth ( ͡° ͜ʖ ͡° )
5. Sangwoo likes making fun of or scaring Bum in public around other people.
6. Throughout season 1 and 2 Sangwoo has slowly introduced Bum to his life outside of the house of some reason. He took Bum to the school festival, introduced Bum to his friends, took Bum out on a hiking date and showed him were he buried his fathers body (he could’ve easily buried Jieun’s himself) and also brought Bum to his work. Maybe its bcuz he views Bum as his pet/property, it’s a tactic to manipulate Bum or bcuz he wants Bum to become more like him.