Only one possible answer: his hair is dry and stiff ╮(￣▽￣)╭
Perhaps tho, coz if we'll look on the last panels, with his side profile, his hair is definetely long so it's quite.... wierd, dunno the word but still it's cuteee coz it's sticking out, talk about balance or what(Forgive me for any wrong usage of terms coz am not a science geek ehehe) (=・ω・=)
I think it's just the artstyle, because YiYoung have always had it. So it's just a part of his main characteristcs (like the eyebrows of Director Kang)
Oh pls don't mind me questioning science amd gravity why the hell I just noticed it a couple of chapters ago that a single strand(composed of a couple strands of hair combined together as one) is sticking out on his head I mean, all washed up and just woke up but that single piece is still there...???
Ps. I know its part of the style, Ahoge, but I jist find it randoml cute and funny asf