I don't know that there's a way to do it "in bulk". I would suggest contacting support and see if they can help. It's possible that they can do a global change and do it all for you at once.
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .