Obviously, a play on negligent homicide.
At its core, the act of vomiting on a person, usually by failure to exercise care that normally would be expected of an individual. This is almost always committed by a heavily intoxicated individual. The guilty party will make no attempt to stop his or herself from vomiting, thus making it negligent.
May also be used to describe an act of throwing up anywhere inside someone's home, on someone's property, pets, car, or any place that makes it extremely annoying or difficult to clean.
The creator of the term has been thrown up on twice, once while talking to the guilty party, and once while driving, and yes, both times were considered negligent vomicide.
"Steve just committed negligent vomicide. He threw up all over the back of Lindsay's head while she was driving."
"Kara isn't looking so good, better keep an eye on her before she commits 'the crime'." (The crime being, you guessed it, negligent vomicide.)
In response to someone vomiting all over someone's couch or coffee table, guy in room says "WHHoooaahh! Negligent!" (May be shortened to just 'negligent' in the heat of the moment).