Team Fortress 2 is Valve's class based shooter released in 2007, and the Scout is its fast talking runner from Boston, voiced by Nathan Vetterlein. His think fast chucklenuts line plays in game when he launches a projectile that can stun an opponent, which made it easy for players to clip and reuse. It spread through TF2 videos, Garry's Mod animations and later short meme edits, where the warning became shorthand for any projectile, prank or ambush the victim clearly should have seen coming but did not.