Ninjat_126's List of "Noobish", Unfair and Game-Breaking FPS Tactics
1) Camping
Sure, you might be having fun with your high powered sniper and your dark corner. But we're hating you right now.
NB: This mostly only applies in TDM and FFA game modes.
2) Quickscoping/Noscoping
A quick/no-scoper can get off a single shot in the time it takes most SMG/AR users to fire a single shot. However, the no-scoper's single shot will kill you if it connects, unlike the other player's gun which takes multiple shots.
NB: This is technically a legitimate strategy and at least puts you on the battlefield with the rest of us mere mortals, unlike camping.
3) Dolphin-Diving/Drop-Shotting
If your hitbox drops to a crouch/prone before your character model does, you'll have to be really unlucky to find someone who can hit you. Fairly common in the Battlefield games.
NB: Not all games have this hitbox problem and the hitbox is actually in sync with the player model. In which case, this is just another bullet avoidance technique.
4) "Noobish" Weapons
Using weapons that are unbalanced, overpowered or just plain unfair will help you get kills, but won't help you make friends. Examples include the "Noob Combo" from Halo.
NB: These are the sort of things that will generally get patched rather quickly, or fixed in sequels.
5) Glitch Exploiting
Glitch abuse includes noclipping into rocks, climbing the skybox and basically exploiting any loophole they can.
NB: These aren't meant to be in the game. If you find a way to hide inside the rock, don't.
6) Hacking
The Holy Grail of players being complete assholes. Granting you unlimited ammo, homing bullets, indestructible skin and the like, as well as cheating everyone else out of a fair game.
NB: Players caught doing this will usually be banned or have their accounts deleted.
I just posted this on the Bethesda forums, wondering if our fine community of Escapists have anything to add or correct.
EDIT: By "Noobish Weapons", I mean things like an Assault Rifle in a World War 1 game. Unbalanced, a bit out of place and completely unfair to anyone trying to play the game with anything else.
EDIT 2: I'm judging this from the point of view of someone out to play some games and have fun, not someone trying to get a huge K/D and a spot on the leaderboards. In my personal opinion, FPS games are more fun when everyone mixes up their tactics and weapons a bit, rather than sticking with whatever they think is the best and kill-farming.