Why does Bakugou drag Kaminari into the bushes and what did he do to him there? I don't understand why he drags him off to the bushes to get him to discharge and go into derp mode. Bullying? To recharge the expensive night goggles? To give the rest of the class something to laugh at?

Can any easy assumption be made to what he did to him in the bushes to force discharge?
Because he wanted to distract the class. That was bagugos money, not kaminari’s. He just overcharged kaminari because he was a good and funny distraction while bakougo paid kirishima back. This display of kindness seemed weak to bakougo and he didn’t want the rest of the class seeing it.