It is very hard to see, but this thread is over 18 years old! I don't understand why CS cannot move these very old threads to an archive section so new threads, hopefully engaging people who are still around, can be started.
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 .