@Psychronia,
@sketchy333 you missed a very important nuance. Clarisse initially chastised the clumsy girl, and THEN her band of troublemakers started using it to bully her.
BUT, when pressed by the main character, Clarisse reveals that she was making a point - in high society, away from this group, there would be actual repercussions at - for example - a tense diplomatic soiree. You could start a war by splatting your cake in someone's face.
Clarisse is being incredibly harsh, because she is trying to teach, not because she is being a bitch. Because of that, all the bullies rally around her. But it looks like she has other people's best interests in mind, she's just misunderstood and hasn't got rid of the bully posse that's ruining her reputation.