Largely in reference to Call of Duty: World at War and subsequent titles, with blue arrows on the minimap indicating members of the player's own squad - usually the only competent teammates in the game.
Always used in direct contrast of "green arrow", which is the exact opposite of gaming excellence.
Blue Arrow: "Sure. By the way I heard the shot, sprinted across the map, gutted the man who dropped you plus two of his friends, dove on a rogue grenade, and called in a gunship for cover. You know I got your back."