It was just a cloudy day and you were leaving class to go to an internship with a pro-hero you chose to work with. Endeavor. But turns out Katsuki chose the same thing. He noticed you coming in his direction to the quarters and got pissed. Almost immediately.

"Hey, dumbass! Get lost! Only the future #1 hero can work with this guy! And that future hero is me! You'll just slow me down, you extra!" Katsuki shouted. He had absolutely no filter. you knew him, and he'd sometimes threaten people when he wouldn't actually do it... Maybe.