I was talking to a friend of mine about the distinction between "rape written to titillate" and "rape written to be unpleasant/traumatic". (I am sure this is a totally normal, everyday topic, and there is nothing weird about discussing it. At least not when one is writing BDSM erotica.)
I am in kind of a strange position on this topic. I enjoy kink, including rape fantasies, but my tastes in written erotica are finicky enough that I don't look for stuff that satisfies it. I say "finicky" because it's not that my tastes are particularly bizarre, it's that it's hard for me to gauge what will appeal to me versus what will squick me. I have engaged in some BDSM, both online and RL, but not a great deal. So while I'm not totally hypothetical about the subject, I am nothing like an expert.
My experience, such as it is, is that there are two separate axes: "Do I, personally, find this erotic?" and "Is this designed to titillate?" I may regard something as titillating even if it doesn't appeal to me personally, and I may find something erotic even if I am fairly confident it's not intended to be.
This is not quite the same as "author intent". For example, someone can intend to write a rape scene as a horrific event, but end up writing it as erotic because that's the only way they know to describe the action involved. But I suspect it's pretty common for the way the author feels about the action to affect the way it's portrayed.
But I do have a lot of trouble articulating what exact qualities differentiate "this is not designed to titillate" from "this is".
To return to the specific issue of rape: I can easily name some examples of "non-titillating rape": Captive Prince (the first book, not the series) and Even the Wingless both contain scenes of rape, and in both cases I not only felt revulsed but felt that the scenes were written to evoke revulsion. I have a harder time naming examples of titillating rape, not because I've not read it, but because what I've read is all unpublished. Either it's stuff I wrote myself, or scenes I watched or took part in on a MUCK, or material from forums or archives I browsed many years ago. Oh, wait, I read a lot of rape in historical romance when I was a teen, except that it was supposed to be romantic so they never called it rape. The Flame and the Flower is a good example of that.
It is not as simple as "is it told from the victim's perspective or the assailant's?" or "does it emphasize the assailant's pleasure or the victim's misery?" Because a rape scene written to be erotic can still be from the victim's perspective and be about how much pain the victim is in.
I think one quality of titillation is the way the action and the victim are described: titillation will emphasize the sexiness of the body and use sensual language. Certainly some tropes are common only to erotica and porn, like the rape victim who comes to enjoy being raped. But it's hard for me to say what exactly distinguishes "this is fetishizing pain" and "this is depicting pain to make the reader feel tortured". I am put in mind of the Supreme Court justice who declined to define what he meant by "hard-core pornography": "I know it when I see it".
Anyway, I write this entire long-winded piece because I'm curious if other people share this same sense, that writing kink erotica is not a matter of what one describes as much as the way one describes it. And, if you do ... how would you describe the difference between the two?