Gosh... I went back to one of those threads Spaw linked to and found a rather short explanation, replete with a poorly attempted joke.... which could be misinterpreted...

"Mine ? I did not choose it. It was the nickname I went by (and still do) when I joined this raucous yet knowledgeable group. It is reflective of my gentle nature and my Hyde side. BTW, it's pronounced g-nu, emphasis on both syllables."

Not that I have a "Hyde" side nor that I am in any way less than a gentleman – well, good ol' boy. Rather, when provoked, the gnu can become a formidable and fierce foe… it's Wildebeeste side. The name was bestowed on me years ago by my cousins who have seen the transformation.