Doesn't Play Well with Others

 is an Fallout 3 achievement on Xbox 360 and PC and a trophy on PlayStation 3.

It is granted for killing 300 people, these can be humans or (non-feral) ghouls. You can check your progress with your Pip-Boy under Stats, then General.

The easiest way to do this is to make a save, then go on a large killing spree. Good places to visit are: Megaton, Tenpenny Tower, Rivet City, Underworld, Big Town, Citadel etc. You'll lose a lot of karma, but that is what the save is for since you only have to hit 300 human kills. You can then reload your previous save, and you will still have your achievement/trophy.

If that sort of thing isn't your style, you could always visit evil NPC-rich areas such as Evergreen Mills, Fort Bannister or Paradise Falls for plenty of people to kill, with no karma penalty. Being good also provides you with a steady supply of random Talon Company Mercs, which become fairly weak later in the game.

Note: Due to reason unknown, you cannot kill any of the kids in the game, that includes Little Lamplight.