In the early days of the video streaming website Justin.tv, before it was rebranded as Twitch Interactive, an employee named Josh Kappa worked there. Josh’s face was uploaded as an emote named “Kappa.” Its popularity grew, and it became the main symbol/emote of Twitch.tv. Twitch users use the emote to convey sarcasm, trolling, or simple mischief, and sentences ending with the word “Kappa” should not be taken seriously.
Kappa is also the tenth letter of the Greek alphabet, analogous to “K”, and it is used as a symbol in many different context unrelated to Twitch.
An example – “It was the most kappa moment of my life” therefore means it was the most sarcastic moment of speaker’s life.
Josh DeSeno a programmer is the face of this now famous meme.
He has a great Q&A available on his website. I highly suggest you check it out and support him at his new company, Fish Bowl VR.