My best guy friend won't talk to me because he's mad?

You have to confront your best friend. If they does not talk to you you have to try hard to get their attention. Write a note to them. Mainly find out what you did wrong. If you find out what you did then you could just say sorry in a letter, phone call, email or text. They are going to have to hear and when they do and if you are sincere then they might forgive you. If it is something small and you have tried and tried, then i guess it is their lose.You did all you could to try to mend the friendship back to where it was, but your friend decieded to not forgive.