You were sitting on a bench, looking at him and waiting for his training routine to end, when a guy from class 1B suddenly came to talk to you. Since you thought he just wanted to have a friendly conversation you obviously answered, but in katsuki's eyes...ohoh, that guy was dead. He was flirting with his girlfriend.

"Oye," he calls out, walking towards you two, his expression grumpy as usual. "Im done." he states.

"And you evaporate, before I blow you up" he scolds the boy.