This is a Greasemonkey version of the Chrome extension called YouBlock by darby.rathbone, not me.
If you're having problems with this Userscript, then do NOT bother darby.rathbone about it on the Chrome extension site or give a poor review there.
To block users in live chat, click the flag next to their comment, and then click "Flag for Spam".
To unblock, just refresh the page. This script does not remember blocked users.