Other than the obvious(bodily fluids for the bathroom) choice. Anything non-con is a very big turn off. Especially when they have the girl portray it as horrible as it is meant to be.
Some people do non-con to dub-con or at least give hints that both parties are enjoying what's transpiring, which is something that is easier to stomach depending on the fantasy. But non-con to the fullest is something I could never stomach and it's something I'm seeing crop up more and more.
Stepbro - Stepsister stuff kind of gets old after the 20th time seeing it... However there was one porn that turned it into a Musical where they sang a song called "A Step Away" and I gotta say... that made it all come together lol