Nerf Ninja 

The act of someone acting like a complete retard only to destroy his own reputation in attempt to gaining one

kid: Hello folks, i am your nerf ninja

others: wow, what a faggot

Nerf Ninja by IamPerson1 December 29, 2009

ninja nerf 

The act of nerfing something without any forewarning.

While most nerfs are announced that they will happen before they actually happen, a ninja nerf is simply done, leaving the players to discover, usually being completely screwed over at the same time due to being surprised.

Player A: C'mon, let's go kill that boss. I'll get my shifter tank.

Player B: Ok, let's go. Those shifter tanks get like 2000 hp, so we should be fine.

*Player A and B get to the Boss*

Player A: omfg Wtf!? I've only got 800 hp!? *dies*

Player B: Oh Fuck... *dies*

Player A: Well wtf... I had 2000 hp yesterday... I didn't see anything about a nerf on the forums, did you?

Player B: Nope. Must have been a ninja nerf.

ninja nerf by H-o-G September 11, 2008