“Just because a principal makes a unilateral rule and its broken , doesnt make it an averiah. it doesnt mean you should break the rule either. Only its not an averiah”
I’m not sure about that. I think it could fall under the category of “zilzul morim”. I wouldn’t ordinarily go over to a teenage girl and tell her that she is doing an aveirah when she breaks the school rule, but if she asks the question, I think it might be appropriate to tell her that she is.
Your giggling example is a bad example because it’s not deliberate. The issue in this case is that she wants to deliberate break the school rules in front of the principal in order to make a point to her. It seems to me that that could be considered “zilzul morim”. You have to respect your principal even if you don’t agree with her. I think that is really the bottom line here. Even if you don’t understand the rule, you still have to respect your principal and her right and duty to make rules as she sees fit.