I think the best condename for a Mary Sue would be 'Poison Ivy'. You should know better than to touch her, and she's so clingy she'll strangle you to death. Apt.
Don't even think about writing something like that. The 'graphic' really has the power to disturb me muchly. I like a bit of angst as much as the next girl but there's a difference between liking to angst several shades of Hell out of a character and wanting to graphically and sadistically torture and kill them. Hell No indeed. And you must heed the call of Karma. Just say no to badfic and all related mental torment. The Gods are telling you that you do not need to read that damn fic again. Once was once too often.
Yup, I can feel a fic like that coming. It'd have to be pretty short, but hey. Youji, Ken and a cupboard with a conveniently temperamental lock = joy in a fanfic box.