The word "Jobby" coming from the Scottish for shit/poo, a "Jobby Jabber" concerns the act of sneaking up behind a friend/foe while pressing both hands together into a "praying" position, then forcibly ramming pointed fingers up the (fully clothed) arse of said friend/foe, shouting "JOBBY JABBER!".
Remember to run away to avoid violent repurcussions;
laughing is
optional.