
Dan was just told not to drink on his medication, the fact that he's continuing would be frustrating for anyone who cares about him. Watching your loved one destroy their life and health is devastating and exhausting-- it's not KD's fault but change needs to happen. And while I think JK doesn't have the awareness to realize WHY KD's choices frustrate him so deeply(aka, just writing this behavior off as annoying or pathetic to avoid actual reflection on why he cares so much), it reached a boiling point. His reaction is far from perfect, but it's a clear and stern response.This is a wake up call for both characters and hopefully a turning point in character development for JK.

I think what OP meant is that since the doctor basically told them that KD might die if he keeps on drinking, him not stopping is like him saying "I don't care if I live or die" and that's what's triggering a strong reaction in JK (= proof that he cares a lot about KD) but since he's bad at emotions, he doesn't know how to express his anguish and worry in another way than getting angry/agressive. The last panels are him properly showing worry/relief = you hug the person you care about/tell them you care about them, you don't blame them/yell at them. But he's fucked up so it'll take time

Would it be stupid to believe that JK won't automatically assume the worst of Kim Dan? He's shown that his personality is completely flawed, and he's selfish. Excuse my word vomit;
But I think that might be just due to how intensely he hides his weaknesses, Kim Dan being one of them. My prediction is JK has caught feelings for Kim Dan, and is fiercely trying to hide/undo that fact by being a POS(which is unforgivable). Paired with his anger issues and personality, this makes him especially dislikeable and selfish.
Moving on, he's made it clear he sees Kim Dan as one of his people, because of that whole arc, I think it might be possible that he becomes the slightest bit aware and realizes what's actually going on. Maybe even getting defensive on Kim Dan's behalf. Alternatively, this would reveal that Grandma is deteriorating more rapidly, and maybe then he'll have the mind to show some respect and empathy.
This is expecting a lot of JK, who's shown himself to be somewhat of a complete narcissist, I know. But I imagine this author will try to redeem JK to some extent by showcasing some form of loyalty.
I also reckon Grandma's favor will become relevant to their dynamic somehow, and that JK has actually read Kim Dan's letter/card.

I'm intrigued by this manga, but the different translators/uploaders is distracting. The watermarks later are obstructive, the cleaning becomes sloppy and the translation starts making less sense. Even worse, some of the pages are jumbled up. I respect people taking their free time to make this work available to us, but the drop in quality has been disappointing as it can make it hard to follow the story.
Thank god for the officials. Thank you uploader!