Yesterday, Katsuki blew an explosion on Izuku's head and when Izuku got home, he realized he couldn't hear anything. He didn't tell his mom, or anyone for that matter because Katsuki would get in trouble with his mother and the school, and that would ruin his chances of getting into UA. Also, Izuku's mom cant affort hearing aids. So Izuku goes to school, deaf. He's at his locker when Katsuki slams his hand on the one next to him, which he doesn't hear

Katsuki: Hey, idiot!