To masturbate out of desperation, especially during an extended period of sexual abstinence. Often the abstinence is not by choice, but rather by one's failed attempts to make it with someone else.
The term originates from an episode of "Two and a Half Men".
"...if you still have the energy, pull it like a monkey climbing the mango tree."
Originates from the term "jacking off" as well as the similarity of the "cracking" sound from performing it and the opening of usually alcoholic beverage bottles.
It is also a popular perversion of "cracker jack", the brand of caramel corn.
Roommate: "You two were so loud last night! I heard you cracking jack so loud I couldn't get to sleep!"
"Yo, she was cracking jack so hard i almost passed out!"