then you unfollow them. and/or you post a special message warning others, and then their software doesn't apply the friend-of-friend rule for that feed.

But to be honest, we havn't had many assholes join (just one, but he left again), so we havn't had to really implement moderation controls yet.
We can't have centralized moderation, which is necessarily one-size-fits-all and doomed to privledge some over others anyway, but instead we can create tools so that a given community can moderate it self.

for example, if you can block or mute someone, you could also subscribe to someone else's moderation. maybe to protect a more at-risk member - say you'll automatically block anyone they block gives them power.

We can't make a system that assholes can't use, but we can make one where you don't have to listen to them. If push-based systems give you freedom of speach, this is freedom of listening.