@neil
I disagree.
User-led options are far superior to server-led controls because the require effort by the user.
I as an administrator do not know (nor really care) what user/content might be "problematic" to another user.
This is the internet. There are people on here you will not like or want to associate with.
If a user is so fragile that they cannot be exposed long enough to block it, then the user probably should not be on the internet anyway.