A referrer tells the webserver the location of the last page viewed by your browser. It is normally sent from the browser to the Apache webserver every time the browser requests information.
This information could be used to control access to your site, for example to avoid others link your site’s images.
Add the following to your Apache configuration file:
RewriteEngine On
RewriteCond %{HTTP_REFERER} ^.+.blockthis.com/.*$ [NC]
RewriteRule ^/(.*) http://www.google.com/ [R,L]
If you don’t understand the above, please take a look a the Apache mod_rewrite manual page. You could also try this very interesting mod_rewrite manual.
Why not just deny the bad guy out of site?