He did not screw up anything. The MC was responsible for that one alone. The MC was really upset because her friend likes Keita. That is not his fault in anyway. Asking that question and a nickname is not the same you have to know that. You can not compare those two. Meanings and motives behind both are too different. I am not defending him but the MC is at fault alone for her problems with Maki.
When it comes to motives, which do you think is better? "Because I'm insecure and feel like I'm losing my best friend to someone detestable" or "because I think it's funny?" As for the meaning, we know that Youko wanted Maki to say that she was more important (which goes with the whole insecurity thing), whereas Keita... likes the name and sees it as a sign of affection, even though it's been made pretty clear that it really bothers her.
And no, if you want to avoid getting into the causal cluster of things, he did not directly cause the issue between Youko and Maki, but he only decided to stop picking on Youko when he thought that he did. Youko being visibly bothered by it didn't stop him. Maki (again, if she even did it) asking him to stop didn't stop him. And Naomi telling him that "Imoko" is a problem and that someone made Youko cry didn't stop him.
It is not about which motive or reason is better. Its about what it the root of the problem. At this point he mostly leaves the MC only and does not bother her. The problem is Youko at this point and her feelings with Maki. Why is he detestable? that is a strong word to use for Ketia. Rude and brash of course but at the moment I will not use such a word. I am only stating you cant blame Keita for everything. At this point we are only going to go in circles so I will say we agree to disagree.
last edited at Feb 13, 2014 2:34PM