when your running down the stairs and your sack smacks your ass.
I was rushing to class when I noticed everyone staring at me because my sack smack was so loud that everyone could hear it.
Similar to sack tap but to a much worse degree.
instead of using a simple flick of the wrist ending with the knuckle, the assailant will use an open hand and strike using the motion of the entire arm, as opposed to a wrist flick.
Damn biatch, your sack smack made me sterile.