At this point in the show, Regina found out that Cady has been scheming against her and intentionally ruining her life. Note that she is at her lowest, since she lost everything that made her the massive deal she is — her hot body (something she was very proud of and willing to rely on), her boyfriend, her followers and, most importantly, her status and her place as the queen bee and leader of the Plastics. After a long moment of meditation and strident shrieking, Regina decides that she’s not going down without a fight and puts her revenge into effect.
Just like it happens the movie, Regina grabs the infamous Burn Book and, for a brief moment, misguides the audience into believing that she’s ready to let it all out about her former friends — but as it turns out, she adds her own name instead, describes herself as a “fugly cow” and prints large number of copies. She then delivers the notebook to the principal and proceeds to frame Cady, Gretchen and Karen for the authorship of the Burn Book, not only putting them at risk of getting in trouble, but also making the whole student body hate them.
The man confronts the three of them about it, while Regina releases the pages as she throws them around the stage. As the students read the content, they start fighting in a hilarious choreographed sequence and wreak havoc. Chaos took over the school, everyone feels angry and betrayed as their deepest secrets and insecurities are exposed to the whole school… But not Regina.
She has nothing to lose. She just wants to watch the world burn and everyone get mean to each other.
