'Mostly' because Monoma has a goddamn talent for inciting Katsuki’s anger. His taunting comments are one thing, but just the sight of his face, all smug satisfaction thinly smeared like concealer over ugly insecurities, disgusts Katsuki. It’s like looking into a mirror in a funhouse at a distorted reflection of what Katsuki could be—had been—and Katsuki hates the reminder. He hates that Monoma always has to remind him of how shitty he was when he started at Yuuei, as if Katsuki’s past year of growth counts for nothing, and he hates that sometimes it feels good to not hold himself back and instead drop down to Monoma’s level.