The fact that you can just... straight-up ignore him. Like... wow... Even if I didn't like him that much, or if I liked Zen more, I'm not gonna be rude and blatantly ignore the greeting he gave me.

And that's not just for the sake of his feelings, although that is one reason. It's also for the sake of my own feelings (I would feel bad if I ignored him) and for the sake of... well. Everyone else can see that! And it usually doesn't go well when people you are trying to befriend think you don't like their friend... especially if you want to get with one of the friends. You know? I wouldn't want someone to treat one of my friends poorly like that...