The line comes from Team Fortress 2, Valve's team-based shooter released in 2007, where the Engineer class builds a sentry gun that enemy Spies can sap to disable it. When that happens, the Engineer calls out the attack in his distinctive Southern accent, and players quickly turned the warning into a shorthand for being caught off guard. It spread through gameplay clips, TF2 memes and short-form edits, and it remains popular because the frantic delivery instantly signals sabotage without needing any explanation.