With the latest patch, “The Black Temple”, it is now possible to ignore and report players who are spamming you by right-clicking the character’s name in the chat interface and selecting “Report Spam”. If a spammer acquires many of these reports, his or her account will be completely silenced for a short period. During this period, our game masters will investigate the submitted reports and may take additional action if it is warranted. Read more about this feature in our Squelch FAQ.
Original post by World of Warcraft Community Site