v.t. - to beat off; yet another term for male masturbation. The term "jank" is a portmanteau of jerk off or jack off and wank or yank or spank. It is often used in the context of derogatory accusation, or as a metaphor for dawdling/wasting time.
I think he went to go jank it one more time before our road trip.
Come on, Dave! Quit janking it and play poker! Call or Fold!
Oh yeah, Eric was totally janking it. I just don't know how anyone could be so horny that they would want to masturbate in a porta-potty.