First, he didn't verbally abuse Xavier, Scott was emotionally close-off from him and made it clear to the Professor, that's because Xavier wouldn't face their real problem and kept trying to go around it and argued about who's in charge (and did it in front of everyone regardless of their argument should remain private), and like Scott said, he needed to concentrate on the mission.
Second, he isn't being a jerk to Prof, his reaction is understandable. Scott was the one who was hurt most by Xavier's betrayal, the one he looked up to as a mentor and a father figure turned out to do tricks, and now he lost Corsair, his trust in Xavier and maybe a brother for this, you expect him to just hug the Professor and let bygones be bygones?
About him blasting Rockslide, I would say that kid deserved it, you don't stand in his way and dare him to move you, because he will, not to mention those kids need to be disciplined long time ago seeing how bratty and obnoxious they were in New X-Men.