Inspired by a segment on hak5. I customized the ClearOS filtered site page to give the users a more entertaining experience when someone tries to access a blocked site.
You can download the custom filter page here.
First backup the original filtered.php
cd /var/webconfig/htdocs/public/ cp filtered.php filtered.bak
Now override the filtered.php file with the custom one and copy an .mp3 of the song named NGGUP.mp3 to /var/webconfig/htdocs/public/. That's it! When someone goes to a blocked site, they'll get Rick Roll'd.