You can delete the entire post. When you reopen the text box there is a button below the text box "Delete Message". Press that, answer yes and the post is deleted.
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 .