Ninja Sack 

A prank that is pulled usually in high school by taking someone's back pack, taking everything out, turning the backpack inside out and putting the stuff back in.

Dammit! The seniors ninja sacked me again.

Ninja Sack by YarmouthClippers June 13, 2009

Ball Sack Ninja 

Type of ninja who use's the scrotum when fighting. Using the fighting style "sack-qwon-do".

He just beat that guy down with his nuts! Damn, He's a real ball sack ninja.

Ball Sack Ninja by benji64 January 29, 2009

ninja-sacking 

an activity taking place amongst highschoolers, in which you...

1. steal someone's backpack while they leave it unattended.
2. remove its contents.
3. turn the sack entirely inside-out.
4. replace the items.
5. re-zip it.
when the owner of the backpack returns, they will most likely be very irritated with you. but they will get over it.

what are you doing to his backpack?" - "we're ninja-sacking it!

ninja-sacking by ashleyvennum December 7, 2010