The line comes from Call of Duty: Modern Warfare 2, released in 2009, where the Tactical Nuke was a 25 killstreak reward that ended a multiplayer match. When a player called it in, the announcer warned the other team with this short alert, giving everyone a few seconds before the blast. Clips of that moment spread through early YouTube montages and forum soundboards, and the warning outlived the game itself. It is now reused far outside shooters as shorthand for any unavoidable, over the top disaster about to hit.