The SourPls GIF comes from a YouTube video posted April 17th, 2007 by user SourNotHardcore (shown below).
One of the earliest mentions of the emote online came January 28th, 2014 by Twitter user @HiredHelp, who pointed out how excess use of the emote rendered the chat unreadable (shown below).
On December 7th, 2014, an inquiry about the meaning of SourPls was posted to /r/Twitch. On March 19th, 2015, the emote was defined on Urban Dictionary as “An animated Twitch emote of somebody dancing, that only works with the Better Twitch TV plugin.”
In July of 2015, interest in SourPls spiked as several users speculated that BTTV had removed SourPls. However, this was untrue. BTTV had recently implemented an update where a user would have to manually turn on GIF setting to make GIFs appear.
On October 26th, 2015, Streamer News mentioned the emote in a tutorial on using BTTV. Blogger CharlieStMonica did the same in February of 2017.