One of my son's was like yours. Showing his emotions often. It was not ever directed towards teammates or coaches, his emotions revolved around his own failures.
He grew out of it (somewhat)
Personally I can't stand that frustrated look some people have when a team mate screws up. However, if you look closely you'll even see it in the Big Leagues once in a great while.
If you really think it's a problem... Take video of him when he shows frustration. Once he sees himself in action he will stop!
PS, I tried this on my wife once. She has a way of replying to "only" me in a not-so-friendly way at times. I would tell her and she would say... You're full of it or something like that. So I carried a tape recorder around and got her on tape. After listening to it she was really nice for awhile. It didn't last long though! Things are back to normal!
