Gangster bump or gangster bumping is when your driving your car you hold the steering wheel with one hand and bump your whole upper body to the beat of the music. You must have you window open and your other arm out of the window.
Its a more extreme version of head bobbing!
Andy: "Wow is that dude trying to remove his car interior!"
Seaward: "No..he's gangster bumping!!!"
1. extremely large pot holes; 2. hole/bump in a street or highway that could potentially pop a tire, crack a rim, or screw up your cars allignment
O damn!! That was a sick Gangster Bump I just went over!