The Rice University Neologisms Database

excellent, exciting, enjoyable This word has undergone metaphor as it seeks to describe the form of a party. Specifically it seeks to describe an excellent or crazy party. The connection lies in the tendency of such parties to have loud music and rambunctious dancing or activity that might cause the structure to shake or appear to be “bouncing” as revelers jump up and down. The connection might also refer to the tendency of such partiers to consume mind-altering subjects that can cause them to perceive excited dancing as cause the house to bounce. It might also refer to the tendency of such parties to have large subwoofers that create massive vibration. The word has now undergone widening to refer any awesome party, regardless of whether or not the dancing is actually rambunctious, indeed, it is not even necessary for there to be dancing for a party to qualify under current usage of ‘bumpin’.’ The clipping of the ‘g’ indicates its likely origin in ebonics where ‘g’s’ are often dropped from ‘-ing’ endings