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

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

ninjanerd

A ninja who is in touch with his nerdy side. You cannot have a female ninjanerd, only male, although they may have feminine characteristics. Used to insult a person who believes he's a ninjanerd, but is a nerd at the same time, the nerd part using the computer freqeuently, the ninja part being stealthy.

"Hah, I am a ninja! But I love downloading this anime and using the computer and chatting on IRC"
"YOU NINJANERD!"

ninjanerd by Mo Hat June 15, 2005