Similar to that of a poonbag, however much more distinct cunt-like behavior. It is said that poonsacks are nearly extinct, yet some still lurk in the shadows of the earth.
- I thought poonsacks were extinct?
- nope, I just saw stephen the other day, he's still alive.
Upon being approached by a guy with a group of females,it is the act of you and your buddies stealing the group of girls from the unsuspecting guy.
Jerry: Hey tom what did u do last night?
Tom: Aw you would never believe, I went out to a club with samantha and her friends and a group of guys poonjacked me.