The popular girl's name was Brooke. She was basically a bitch, especially to the jocks who wanted to ask her out. You figured that you, and the rest of the men of the school have suffered enough from her, so you decide to write her down in the TF-Note, as you open the first page, and see what could happen.
You start by writing her full name down, which was Brooke Milton, along with the description of her face. Once that was finished, you try and figure out what to change about her. Seeing how she's been rude to almost every guy in school, you decide to punish her with something that could destroy her popularity, and basically shatter it completely. So all you decided to do was brainstorm of away to change her life with misery, without getting caught that is, and you figured out what to do.