From "Coffee With Sargeras", the Sargeras Emote is a whopping 6-character emoticon used only for the most colossally, life-alteringly incredible statements, situations, or instances. It is as follows:
>>}8^O
The Sargeras Emote can only be used for things where no other emote could possibly convey how catastrophically awesome its attached information is. Misuse will force Sargeras the World-Eater to come down from the Twisting Nether and consume you and 4chan. While nobody would miss 4chan, you'd probably like to keep your own life, so figure out some other way to get rid of /b/.