mDz, please. Don't let your friend down, he isn't what you have described. And beside, we 3 play Gmod together so don't act like you haven't met him before.
As for Grin:
He is an easy-go person. Yes, he has some problems with his anger, but he can easily change. For example, yesterday he was pissed off at some lagger and as usual he would start raging. But PMing him and saying that it is not a good thing to do and that there is a better way to deal with it, he stopped raging and he managed to beat the lagger the way I told Grin to do it.
Instead of you VUs just kicking/accepting players just like that and hoping that the person will find a way to change his character, you can just give him a tip or two and he should take a hint or smth. Ye I know - it's not my business but I'm just giving my opinion.
So I think Grin should be given a chance, give him a tip or two on improving his behaviour and you should end up with a damn good player. Not to mention his skills...
Good luck, Grin!