Referrer
There are times that you want to block referrer, here is the perfect code for your htaccess file:
# SITE REFERRER BANNING
RewriteEngine on
# Options +FollowSymlinks
RewriteCond %{HTTP_REFERER} badsite\.com [NC,OR]
RewriteCond %{HTTP_REFERER} badsite\. [NC,OR]
RewriteCond %{HTTP_REFERER} sub\.badsite\.com [NC]
RewriteRule .* - [F]