[Full disclosure: I was involved in one of my not-so-infrequent "debates" with a BT troll, and stumbled onto this question. I questioned that the name of Nasty K came about less due to Natasha's reputation as a vicious combatant, and more because of the "Hot Chick" perception perpetuated about her due to the Tales of the Black Widow cover. I'm honestly not sure where the term even originated and when.]
So I'm asking here. Anybody with access to some of the oldest fluff material...was this name actually used in canon material? If so, where? And when? Was an explanation for the name ever given?