How do I ignore forum users completely?

Most forum boards have the option to "ignore" users who posts you find pointless to read. However their name still appears in the thread with a little message:

You have ignored Idiot. ::View this post:: ::Un-ignore Idiot::

If you're using Firefox you can remove their post from your view completely.

1. First install Greasemonkey.
2. Then install Cortex's "Remove ignored posts" greasemonkey script. Available here.