It is hard to tell exactly the situation(s) that you are describing in which he gets very angry. Is it only when he's playing with his friends like that OR is that just the way his friends behave and you are concerned that the behavior is rubbing off on him in other situations?
Here is what I think... I had "temper tantrums" throughout my childhood. Not many though, and other than those I was EXTREMELY well behaved like your son. I also had trouble as a young adult with "temper tantrums", so I took myself to a therapist. I found i was acting out on desperation. Then remember that, yes, I did very well believe that I was not being taken seriously and that no one understood me or believed me in certain situations. I was the youngest and my opinion seemed to be pushed aside cause- "what does she know?". I did have a high IQ (144), and made straight-A's, but instead of that giving me credit, it just made things worse for me, because I KNEW I knew things, and no one else thought I did (or so I thought). I also had troubles that I told no one about (I was sexually molested throughout my childhood by my grandfather) that was hurting me inside. On top of THAT, I grew up with a bad example on how one expresses themselves by my angry alcoholic father (who really wasn't a big part of my life, however...)
Perhaps (and I hope) your son doesn't have all those factors up against him, but maybe he has some sort of feeling of desperation. At that age, kids feel older and they know that they aren't "little" anymore. They know more. Perhaps with this knowledge he is dissatisfied with his standing in the family. Maybe give him more responsibilities. Have him know that you respect him and believe in him and trust him. Also, triggers to this behavior can be unbelievably small, but still- keep an eye out for the triggers. And as well, know you are there for him when he has those fits. Of course don't encourage that, but also let him know that even when his behavior is ugly, that you still love him (although YOU know you still love him- at those times of irrationality me may convince himself that he's alone and unloved).
This is just some kind of "guess" of mine... since I didn't get a good idea of the situation you were describing. Hope this helps.
OH- another thing: I don't know if you have told him or not, but don't tell him "I want my sweet boy back" because I have a strong belief that it further distances yourself from him... Kids take that saying in a totally different way. It worked very negatively with me when I was told that, and I've known other instances where it noticeably bothers the child (oh- I majored in psychology in college- so this is coming from what I've studied as well as experienced)