When either a man or a woman squats over the ass of another and shits on said ass and then proceeds to push the fresh shit into the others ass. After completing this task, the receiver then gets up and shits their feces and the feces of the shitter into the shitter's mouth.
Me and Nik were out in the back and he gave me the worstgravytrain.
The small amount of extra weight on a girl that could still be considered "sexy." Baby fat can also be considered "Gravy" as well. Fat on a girl that is unatractive on all levels would then be considered "Paint" ....