The Rice University Neologisms Database

To steal or borrow another's possessions without permission. Jank has a similar meaning to the word steal, although jank does not carry as strong connotations as the steal. Unlike steal, jank implies that the item is being borrowed temporarily, albeit without the owner's explicit consent. Although janking someone's belongings is done without permission, the owner most likely would not be offended if he knew. The word jank was used because no other word exists in the English language that means to borrow without consent. The two root words that make up jank, jerk and yank, reinforce the idea of taking suddenly without permission. Additionally, jank may be related to the word jack, which sometimes means 'to steal.' Jack, however, carries a more forceful meaning than that of jank.