Facebook privacy shortcuts provide a quick way to block unwanted contacts.
Here is how to do that :
Click on the lock icon at top right on Facebook and choose ” How do I stop someone from bothering me?”
In the “Add name or email” field, enter the user name or email address to be blocked and hit Enter.
This will display all the user names as per criteria, simply click “Block” next to the user name to block them.
This will prevent the blocked users from messaging you, being on the friend list or viewing your status updates.