My FAVORITE line still is such a simple one, easy to overlook: Episode 9: "Jun Wan, if you have time, would you please get lost?" I love them being cheeky with each other.
Also from #9 (25:45 or so), Jeong Won to Ik Jun: "You borrowed 10,000 won, 4 cigarettes, and 1 lighter." //Ik Jun: "Hold on. [singing] 10k won, 4 cigarettes, and 1 lighter. Jessica, only child, Illinois, Chicago. Ahn Jeong Won from school is such a cheapskate." Parasite reference.
Episode 10 (in addition to what was already mentioned, the confession to Song Hwa about what Ik Jun does for himself): 1) The Wangsimi monologue Ik Jun spills out. 2) The car confession to Seok Hyeong with the final bit to it being "don't pretend this didn't happen tomorrow."
Episode 11, 32 mins in, Jun Wan to Ik Sun: "Who said I had a ring or necklace?" followed by giving her an earbud to listen to, the ring looked at later longingly.
Oh, and elders' mafia game... can't deny it is a lasting love there. Rosa and her BFF are so natural if someone told me they DID know each other 60 years I wouldn't even be surprised!