Facebook allows the users to block a person by email or name. This would mean that the person can no longer be your friend or interact with you on Facebook. To block a person, click the Account dropdown arrow and select Privacy settings.
Under Choose your Privacy Settings, navigate to Block Lists section and click on the Edit Lists.
In the Block users section, enter the email id of the person who needs to be blocked and click the Block This User button.
The blocked user would then appear below the Block users section as shown below. if you want to undo the change click the remove link that appears next to the person email id.