People on my Flist have probably seen me post about this fic before, but I post it again because I still swear it is one of the most possibly unintentionally entertaining things I've ever read, and I've yet to see it mentioned elsewhere:
Perfect Green. Vexen/Repliku, although confusing for using 'Riku' as a name for the Replica for a good portion of the story and at awkward moments. NSFW, and possibly not safe for brains, but deserves to be immortalized for lines of (as aforementioned) unintentional hilarity, such as:
Through his climax, Vexen jabbed away at the Replica’s prostate.
and
Vexen hit the Replica’s sweet spot, which he remembered installing with great care.
and
The replica dreamed fabulous dreams of evergreen forests and killing keyblade-wielding supermodels and finding Vexen’s heart that night.
Intellectually, my brain tells me this is badfic, but the narrative choices entertain me too much to really make me care. After reading
Slave Bear of Care-A-Lot (er, also NSFW. and definitely not safe for brains XD) it just sets a standard of wrong that nothing else can breach.