Im pretty sure this chapter is all in Punpun's head. The guy he was beating up looks like sachi's drawing of his face and they both have the same fit on. Him beating up the guy is just a metaphor for how much he hates himself. The one thing I cant seem to wrap my head around is aiko's perspective in all this. When she stopped him was it because he was harming himself? And when the guy smashed the car windshield was it punpun doing it? I mean he was also drawn inside the car. Another posibillity is that he really did beat up the person but everything he hated about him was a also just projection of what he's done wrong in the past and thats why they looked similar.