screen peeker
Term used in any multiplayer fps in which the screen is divided into "sections", each section being a viewpoint for each player. A screen peeker is one who looks at another player's section in order to find out the approximate location of said player, as well as to make sure no one is following them or has them within their sights. This gives them the advantage of knowing where the enemy is along with knowing when they are in danger. Generally it is a frowned upon tactic, but there are some who approve of it.
Player 1: Dude, there is no way you could have known I was coming up behind you! You're such a screen peeker!
screen peeker
One who glances without permission at the computer screen of others, usually done in public and to laptop users.
"I was trying to log onto Facebook but there was a screen peeker lurking behind me so I had to close my screen and walk away."