So what if Bakugo just fails the entrance exams.
He blows up at another examinee and parts of his robots fall on other students so they just straight up fail him.Bakugo starts wandering the streets during the day and after classes just being aimless and angry. He gets into random street fights to blow off steam.
It takes him a while to realize all the fights he's getting in are actually small time crimes like muggers and gangs. He just wanted a fight. Hes being all self depreciating since his dream school had to highlight to him that he doesn't have any trademarks of a hero except a strong quirk, his behavior was "uncaring of bystanders" and "forgetful of the fact that heros first priority is the rescue"
His dense ass doesn't figure out that he's become a vigilante until someone names him or it shows up in the paper (actually even if it was in the paper he wouldn't realize it's him)
He then has to deal with the realization and decides to just commit to it. Hes already been kicked out of hero school so not like illegal activity is going to mess that up for him now. He also realizes that how he was is wrong but is slightly at a loss on how to fix it past punch your feelings out.
Hes a violent vigilante so they of course try to catch him but he doesn't use his quirk unless he's touching someone and absolutely needs to know order to throw off the description. He also sticks to more afternoons and early morning instead of the usual night vigilante stuff cause its easier to leave and blend into a crowd than try to hide his explosions at night.
I really want his vigilante name to be something ridiculous like "punch therapy" since he punches people back onto the straight and narrow and everyone can tell hes punching his feelings out.Maybe we get some dadzawa.
Maybe another hero gets a shot at taming vigilantes.Who knows it could be a fatgum thing?
Izuku meanwhile flourishes at UA and doesn't break himself everyday. Hes popular and discovers how to work his quirk while comparing notes with Kaminari who by comparison learns to concentrate his quirk vs spreading it out.
He never takes up the name Deku as no one's calling him that anymore. He really steps into himself without having someone yelling at him all the time.