Team Fortress 2 is Valve's class based multiplayer shooter first released in 2007 as part of The Orange Box, famous for its nine mercenary classes and huge library of expressive voice lines. Short callouts like this one later spread far outside the game through YouTube edits, Twitch streams, Discord servers and soundboards, where players clipped single reactions to reuse as jokes. The oh no line survived because it is instantly understandable without context, works for almost any class or character on screen, and matches the game's bright, slapstick tone.