The phrase comes from online slang where yes sir gets stretched into yessirski and then yesssirskiin for extra emphasis, a playful twist popular in gaming chats, streams and short form video captions. The longer spelling mirrors how the voice drags the ending, making it easy to recognise in text as well as audio. It spread as a reusable reaction rather than a line tied to one scene, so creators drop it over wins, dunks, edits and confident replies where the joke is the over the top agreement itself.