This guy's a total jerk. But, the real reason he's going after Mutou-kun is not that he's jealous or narcissistic as such. It's that Mutou-kun represents a direct assault on the guy's cynical mental model of the world. That is, he doesn't have a face at all and yet there's this cute girl clinging to him.
But the thing is, the reason he's so grumpy and spiteful is that he's not actually happy with his cynicism--he wishes the world were a different, better place and takes out his disappointment on the people around him. So like, in the end he's going to give in and be happy that Mutou-kun and Kaori are good folk. Happens every time.