What It Means: Holing up in a reasonably secure location, waiting for the hapless n00bs to approach, and serving them a nice tasty lead salad.
Why You Hate It: Unless you go all the way around the map, there's only one way to get at the super death ray, and it's right past this path; but that guy on the other team simply insists on gunning down anyone trying to use it. Why the hell hasn't he run out of ammo yet?
Why You Do It Anyway: Because it works, not to put too fine a point on it. Sure, in your heart of hearts you know it's not really fair, but this is war. If you can kill the other guy without him being able to kill you, then the hell with a sporting chance. Your K/D ratio is much more important than his.
Besides, you'll be damned if you're gonna let the other team have the super death ray.
What It Means: Really? Okay, for those of you who go out of your way not to know things, sniping is using a long-range weapon against some poor bastard way over there, and dropping him without him ever being the wiser.
Why You Hate It: Half the fun of playing this game is getting to watch the guy who thought he was a badass crumple at your feet. Face-to-face, when you're the crumpler, you can see the crumplee. When the roles are reversed, at least you know you lost a fair fight to a superior opponent.
Getting sniped changes everything. You don't even know why you're dead there's no one anywhere near you and no grenades went off. It's pretty damn hard to defend yourself against an enemy you can't even see.
Why You Do It Anyway: It's quick, easy, effective, and involves almost no danger for you. Basically you become the hand of God, smiting the lesser beings who dare to challenge your supremacy from a place of complete safety.
Shot in the Dark
What It Means: Firing wildly and, through sheer luck, killing the guy you were almost aiming at. Also known as the 'poke-and-hope', the 'spray-and-pray', and 'GOD DAMMIT HOW DID THAT FLAILING MORON GET A HEADSHOT!?'
Why You Hate It: At its core, every FPS is a game that should require skill and practice to get better at. The Shot in the Dark throws that whole concept out the window, and lets pure chance strike you down. It can take a seasoned veteran and cause him to lose his streak at the hands of some no-talent, button-mashing asshat. Or, even worse, some dopey 7-year-old whose knowledge of the game doesn't stretch beyond 'this is the shooting button'.
We play FPS as a temporary respite from the real world; another reminder that the universe hates us is the last thing we need while gaming.
Why You Do It Anyway: In your defense, you don't really mean to. This behavior is easily the most forgivable, due to it often being honestly accidental. If a guy gets the drop on you, sometimes just throwing a whole clip at him in a panicked frenzy of gun-waving is really all there is left to do.
What It Means: Well if you don't know, I'm certainly not going to tell you.
Why You Hate It: You just locked digital eyes with your foe. The two of you shoot it out for 10, maybe even 15 seconds. After the epic battle, he honors your bravery and skill by droppin' his nuts right in your face.
It's the FPS equivalent of Achilles dragging Hector around the walls of Troy; you already killed him, dude. It's not like he's gonna feel it, and pretty much everyone that's not you thinks it's a dick move.
Why You Do It Anyway: Some ancient Fijian cultures used to eat their slain foes. You know why? Because they believed the man they killed belonged entirely to them now.
It's the same mentality in FPS. You beat him. He was alive, and now he's dead. Because of you. Since most FPS do not permit you to steal your opponent's soul to make yourself stronger, tea bagging is as good as it's gonna get.
What It Means: Spouting pure, vicious hatred over a headset so that guy on the other side of the console hears, in exquisitely malicious detail, just exactly what it is you're going to/already did to his mother.
Why You Hate It: At this point, gamers have become so accustomed to the malevolent fury of the other guy that it's mostly just noise. That guy has to have a unique mix of anger and creativity just to get a sarcastic reply out of you, let alone a stunned pause followed by an impotent "Nuh uh "
Why You Do It Anyway: Well, that guy just got pwned so hard, there's a pretty good chance he wasn't paying attention. You should probably let him know what the hell just happened to his world.