I'm guessing Kitami's doing this as a mirroring of what Kanzaki & Fuwakara put Himari through the day before graduation.
I'm curious, though, if Himari will show up and stop it. It seems the line being revealed is that Kitami was the one behind the Tojo-chan Avatar, at least in a big way when it comes to these punishments (like what happened with Fuwakara, especially). But Himari seemed rather distraught when she was confronted by her manager, and the back-and-forth between her and Kitami from there seems to suggest that she's trying to find out what all Kitami's done in the name of "revenge". And with Kitami confronting/accusing his mother in this chapter, I wager he holds the biggest grudge of all, and it's festered to the point he's murdered one student and tried to kill a second (can't believe Furakawa survived that fall).
So my guess is that Himari is the character of actual pure goodness, and Kitami is the "vengeful" one who's been punishing all of Himari's tormenters. Which would mean that if Himari wasn't privy to the extent Kitami has gone to until just recently, she might try and prevent whatever's about to go down, to reinforce that she's "good & pure". Even if tormented by Kanzaki, Himari wouldn't want the same thing done in the name of revenge; Kitami is the one who is "falling from grace" by getting his hands dirty and actually carrying out the vengeance and the punishments, and is now taking it too far (in Himari's eyes).
Getting near the end, though; it'll be interesting to see how this all shakes out.