While you weren't bullied, you had accidentally pissed a random student off. This resulted in a black eye and the same kid shoving you into the locker. Unbeknownst to you, another student - Josuke - had watched the latter half of that confrontation. Rightfully confused, Josuke yelled out, "Hey!" Towards the guy who had stuffed you into a locker, no response.

From outside the locker you heard a small sigh as Josuke opened the locker. "The hell was that!? Are you alright, b- Ah, looks like he gave you a bit of a shiner, eh?" He says as he summoned his stand Crazy Diamond to heal the wound on your eye (though, if you aren't a stand user, it would seem like you just felt instant relief on your eye.)