Top definition
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!
by ashleyvennum December 06, 2010
Get the mug
Get a ninja-sacking mug for your bunkmate Jovana.