I first heard this sound from DarqShado, and although he may not have coined it, he certainly brought it into widespread usage on the channel. It describes the sounds associated with anal sex -- if you're a top, it describes the rhythmic grunting sounds; if you're a bottom, it describes the sound your butt makes as air is forced out by displacement. Number-6, who makes a habit of making nouns into verbs, started using *unf* as a verb (usually in series, e.g. "Number-6 *unfunfunf* Morph|ne"), and in common usage, *unf* is both a sound and an action. DarqShado also observed that "...when you *unf* repeatedly, it always starts to look like fun..."