He opened his mouth to protest but realized it wouldn't do any good. She didn't want anything to do with him like this.

His shoulders slump and he tries like hell not to look disappointed. Or worse hurt. Even though he feels like shit about this whole situation.

Which of course means that instead of letting himself acknowledge that pain, he'll just cover it up with bullshit anger. Because it's better to be angry than hurt.
His posture changes to reflect that, shoulder square again and he sets his face in a carefully neutral expression.

So fine, fuck her! If she wants to be a bitch let her.

"Yeah, sure. See you around."