Not everyone abides by the rules of Stack Overflow. Sometimes they abuse the system by insulting other users as well as down-voting their questions, among other things. It would be nice if a user could have blacklist, perhaps enabling read-only access to that group of users.

This would not only help the victims of those users, but also Moderators, who constantly have to intervene to resolve petty conflicts, becoming a bigger problem as the community expands.