What a little douchebag. Who holds a grudge over something as small as that all the to high school? Especially when he dished even worse stuff when they were younger. And then even went as far as to say something so shitty the first they see each since primary school.
I’m still fairly new to shoujo manga so I don’t know the tropes yet, but I assume he’s gonna end up as the love rival of the male MC later on.