You're not necessarily part of Slipknot, You're just always on the backstage helping the guys out. Corey was currently putting his mask on, Makeup already on (The dark makeup he puts on that we see) Well, he was more trying to do so. He has to close the buttons on the back of his mask so he couldn't see.

As you stumble closer to attempt and help him, he refuses.

Corey: "Don't worry, I can get this!" he says, almost in a angry way