Eunyung has the kind of personality that rubs people the wrong way. People are too busy being angry with him to really think about his situation. Look at it from Juwan's point of view. Juwan got home and Haejoon was very ill, probably mildly dehydrated and he hadn't eaten all day. Eunyung is just sitting there and hasn't done anything to help Haejoon. As readers, we can see the signs that Eunyung probably came from a broken if not outright abusive home. I mean, he was introduced while living in a tent so clearly there's something wrong. It's also bizarre that he doesn't understand how to take care of a sick person, which implies no one has taken care of him before. But Juwan doesn't know all the things that we know about Eunyung and the two are constantly in conflict. I think Juwan comes off as annoying because he has the most stable home life and his problems come off as trivial in comparison to the others. Juwan himself is aware of this. He was complaining that his mother is annoying to Haejoon, who then reveals to him that his own mother is dead. You could tell from the look on Juwan's face that he regretted saying all those things.