BlackHeart Biohazards

Further Fudanshi terminology research:

according to Japanese wikipedia (machine translated)

Fudanshi , all- name fudanshi (Japanese: fudanshi / Fudanshi Fudanshi ) , yasaku fudanshi ( fudanshi / fukei Fukē ), fujoshi ’s lyricism, Sokushi-kiri BL , Bara , Yaoi ’s works men [1] . “Rotten brother” is a model of “parents” [1] , appeared in 2002, first seen on PINK channel ( Japanese : PINK channel ) 801 board [2] . 

translated from:

腐男，全稱腐男子（日语：腐男子／ふだんし Fudanshi），也作腐兄（腐兄／ふけい Fukē），為基於腐女衍生而來的詞彙，即指喜歡BL、Bara、Yaoi作品的男性[1]。「腐兄」一詞則是模仿「父兄」[1]，2002年出現，最初見於PINK channel（日语：PINKちゃんねる）的801板[2]。

So from this, we can glean that the term “fudanshi” first gained usage around 2002, on Japanese imageboards. Specifically PINK channel which was an adults only imageboard.