Is there a tradition at your child's high school?
At our kids' school the seniors pick a day near the end of school and all show up early and park side ways to fill the lot. Annoying, but harmless.
They also sent a mass text to the freshman class that at 12 something, during lunch everyone in the school was going to lay down on the ground as a joke on the teachers. In reality the only ones who laid down were freshman.... jokes on them.