When everyone was making fun of Naruko in class, Ginta turned around and realized that she was writing something in her notebook. What was she writing?
Her notes are translated in the fansub version of the episode (click on the images to enlarge):
Here is my own translation of the notes, since the fansub translation above missed some of the characters, resulting in slight deviation of meaning:
It's not like that. I didn't do it!!
Don't just say whatever you want!!!
Shut the hell up!! [Note 1]
[Note 1] A word or two are missing at the beginning, probably 永遠 (forever, eternity). The translation here is my own preference.