The next day, right as the bell starting seventh period rings, Nick raises his hand and informs Mrs. Granger that he forgot his frindle. One of Nick's friends makes a big show of digging a pen out of his backpack, tossing it to Nick, and Nick continues the charade. The other kids laugh at the funny new word while Mrs. Granger glares at the class. After class, Mrs. Granger asks Nick to stay for a moment and chat. She tells him not to interrupt her class with his funny idea and Nick tries to look as innocent as possible.
Again, Nick is the ringleader here, but his friend is an essential player in introducing "frindle" to their classmates and Mrs. Granger. It's telling too that "frindle" elicits laughs. As a funny word, it's far more likely to capture the imaginations of a class of ten-year-olds and spread. Mrs. Granger's displeasure suggests she knows this and sees this as a dangerous thing.
Mrs. Granger holds up her favorite maroon pen and explains that she's talking about pens. Nick makes sure his eyes are wide and blank as he insists that he honestly did forget his frindle. Mrs. Granger purses her lips and releases Nick. As he races out of the room, he promises to never forget his frindle again.
Standing up to Mrs. Granger like this shows that Nick recognizes that "frindle" gives him a lot of power. It's not a bad word, which means that there's no real reason why he can't use it in a school setting.