
one of the things that irritate me so much is that jk is much younger than dan yet he keeps using informal ass fuck korean when dan still uses 습니다 and never disrespects jk once

That bothers me too, and I feel like even when we get to the point of the story when they've resolved everything Dan will continue to call him Mr. Joo. I'm not really sure if it's a cultural thing, but perhaps the difference in their social standing (in terms of wealth) is something that will always be acknowledged notwithstanding their personal relationship.
FINALLY FINALLLYYYYYYY