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Actually it was weirder that ML kept holding onto that grudge and toyed with MC a decade after it happened, as some kind of petty revenge. I mean sure, to a teenager it's pretty upsetting to hear that they aren't pretty/handsome enough for their crush, but MC wasn't cruel about it. He simply said "no, sorry" and told him why. He didn't laugh at him, didn't mock him or insult him. He took his time to properly reject him, despite being called away, and that's it. Yet ML was a jerk to him after such a long time, despite still liking MC and obviously knowing that MC likes him, which should have been something to be happy about. Weird.
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Not everyone understands tactfulness at the high school level- remember that incident happened in HIGH SCHOOL NOT NOW when they are adults. But then again everyones' experiences during their school years are different. If all your classmates were tactful and sweet good for you, but for the majority of us- not so much.
So we all gonna forget about "face is everything to me" situation? something like leave past in the past?