In my little corner of the world, it's not as easy as "tattling" on a player. You're only caught if you get busted by the police. The police are required to report incidences to the high school.
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 .