John City

NERF
To weaken or make less dangerous. Taken from the "Nerf" brand name, which makes sports equipment toys out of a soft foam (e.g., the Nerf football is soft foam rather than the hard leather of a real football). Used frequently in the context of computer game balance changes.
"The chaingun was awesome til they nerfed it, now you can't hit shit with it."

NERFED
The term "nerfing" comes from the online gaming world of Ultima Online.
At one point in the game, the developers reduced the power of swords in melee combat.
This resulted in players complaining that it was like they were hitting each other with nerf bats, not swords.
From then on, if ever made less worth while than it had been originally, it is considered 'nerfed'

NERF HERDER
A lower class outdoorsman who spends his days safeguarding the nerfs