This reaction comes from Stickman Battle Round 3 Blue vs Yellow, a Flipnote Studios animation built around a fast stick figure fight. The line is spoken as the blue and yellow characters trade blows, with the narrator reacting in real time to a kick followed by a throw. Clips like this spread through reaction and meme soundboards because the voice is easy to recognise and instantly signals shock. It remains popular for short edits where a single oh my god moment needs to carry the joke without extra explanation.