Anger left his body as he felt he had to do something terrible. He held his mask in his hand, Snoke's words running through his head after their last meeting..

You're no Vader.. you're just a child in a mask.

When he heard the word about the mask, he hit it with all his strength against the wall, a few times quickly, some sparks flew out of it due to the lighting. Why did Snoke praise you and not him? He was disgusted by this and already considered you a rival.