All you need is to login into your Facebook user account.
Go to Privacy Shortcuts and click on it. A drop-down menu will show, Click on How do i stop someone from bothering me.
When you click on How do i stop someone from bothering me, it will expand showing you a text area for you to type the email address or Name of the person you want to stop from bothering you.
When you are done typing the name or email address of the person you want to stop from bothering you ,Click on block.
Another popup dialogue box will open for you to confirm the name that you want to block.
If that is the right name then go ahead and click on block if it is not the name you intend to block then close the dialogue box and retype the correct name or email address of the person you want to block .
Source:Seebgh.blogspoot.com
