A specific form of male masturbation where you slap your dick from side to side between each hand until the preg nog is released. (Technique usually hits its usage peak from around December 1st through December 7th.
Dan got so inspired while baking sensually enticing pancakes for breakfast on December 1st that he decided to Flap his JackJack before sitting down to a nice meal.
You have your left turn signal on and are clearly trying to merge into the left lane; instead of slowing down to allow you to change lanes, the Jackwacker behind you speeds up to block your access. This guy is a complete Jackwacker; he sucks at life.