'Jabangr' is an abbreviation of the question: 'did you bang her?' It is used as an immediate response to friends of yours who are talking about various girls/women they've met and/or been on dates with. It's not important whether or not you care about the person actually banging the girl.
Unlike the actual question--"did you bang her?"--which is intended to elicit an answer--the abbreviated phrase is used more as an interjection designed to introduce the thought that maybe you should have thought harder about trying to bang the girl.
Paul: "So I met this girl last night..."
Brett: "Jabangr."
Paul: "Ha, no we had dinner, but then afterwards one of her friends showed up, and..."
Brett: "Jabangr."
Paul: "Man, what a panoche you are."
aka J-Banger, the dear leader - supreme overlord, whatever you call him; he's omnipotent. He's everywhere; act like he's watching.
jbanger dot com, incredible imagery
Person 1: "Hey man, I saw a bunch of JBANGER posters and stickers around the place. I even saw someone wearing a shirt, whats that all about?"
Person 2: "Yeah, the following has grown. Billboards are next. Have you seen the website? All hail the leader, JBANGER!"