Butthead her.

You hit your forehead into her nose, causing her to stumble back and release your balls. She didn't hurt them much yet, but it felt pretty humiliating, especially with the eyes of other students on you two. You decide to pay her back the same way.

Before she could recover, you grope her between her legs. But instead of going gently like a you did to your girlfriend, you grab it and start twisting and smashing. She squealed in discomfort and tried to pry your hands off her soft groin, but your hand stuck like glued.

Still, it wasn't enough for you. You stuff your finger into her pussy through her pants, ripping a hole in them, and start moving them back and forth rapidly.