A unique and way to hit a male in the testicles. Not a full-on slam to the scrotum, but instead produces an aching in the balls, depending on the intensity of the woppo and the skill of the woppoer.
Think of the idea behind cracking a towel. By quickly snapping the wrist back, the end of the towel picks up a massive amount of speed and energy, creating the snap and a welt on whoever recieves the end of the towel. You will be doing the same thing with your hand, except your wrist will be the pivot point, your fingers are the end of the towel, and the person on the other end will instead be some unsuspecting male's family jewels.
First and foremost, the woppoer must have an element of surprise. I always keep a look-out for any possible danger to my man-ovaries, and so should most males. But to sucessfully give someone a woppo, you must be sly.
When you are in position (hand and arm in good relation to the junk, as if you were to grab it), and pull your hand back about one foot or less (you want to remain mostly unnoticed and undetected, so no more than a foot) from the berries. At this point, your wrist and fingers should be totally slack. Bring you hand at a fairly fast speed towards the boys. When a good distance from the target (about 4.5 inches or the averaged length of your fingers), snap the arm back towards you as fast as possible. The tips or front half of the fingers should hit those dangly bits with quite an amount of speed. The initial response may be anger or annoyance, but the real aching pain won't hit the gonads until a few minutes later.
This
move should be
used with care, and is suggested to only be excercised among
good friends. Although the
intended targets are the
naughty bits, since you presumably can't see
where they are in
relation to the
purple-headed yogurt slinger, any woppo to the
genatalia will do
just fine.
Note: In some circles, this may be known as a sack tap, which is also a skateboarding term.