The 360 Quick Scope is a difficult technique but often used in FPS games (Call of Duty Mainly). Is that a player with a sniper rifle, taking into account their aim sensivility is on "Insane", move the right stick to the right or left and the player starts to move the aim quickly and remain in a situation which can go dizzy until you have a lucky shot and kill an enemy. In fact, it takes more than 360 degrees to kill someone, because it is very difficult to know exactly where you're going to shoot and takes a little longer to get ready. The 360 Quick Scope is used frequently to presume the players and basically, people do this is a Final Killcam.
*A Player do a 360 Quick Scope and kills the enemy player*
Enemy player: "That guy is insane! He used a 360QuickScope to kill me, that sucks..."