Sounds like your BF is trying to be a good dad, as best he knows how. That's a good thing. On the other hand, the kid sounds like a hyperactive 9yr old with discipline issues.

I've been there, except the kid was a poorly behaved girl.

Talk to your BF about it, addressing the hyperactivity and need for rules. He is the one who must impose the rules with his son, otherwise you become the bad guy. Once rules are established, you can help enforce them by reminding the kid of the rules, if the need arises. This won't make you very popular with him, but it's better than being the wicked witch. Also, the kid may need some medication...obviously an issue for your BF to discuss with his ex...but you may want to bring it up.

In any event, good luck. I know it ain't easy ;-)