@Janeece ,
All schools have rules but those rules can differ school to school or even just a change of principal can lead to rule changes. Normally, some of those rules will apply inside or outside on the school grounds. As Sturgis suggests, you can contact the administration. I'm not sure what a "dean of students" means. Is he/she a student or a senior teacher?
But in any case, my opinion is that the person behaved inappropriately in taking your drink and throwing it away. There's no harm that will come from a beverage out of doors. If you're mad, I don't blame you.