Well, I don't like to see violence or anything beyond the standard, conventional ideas of what "rough sex" is (ass-spanking and MILD throat-grabbing and hair-pulling). To be more specific, I don't like to see women having their faces slapped, for example. Lame. There's absolutely nothing arousing about rape or simulated rape. It's a crime, and for good reason.
As for aesthetics and turn-ons/offs, I don't like to see gaping assholes (although anal sex is arousing to see, but the post-sex focus on the colon is just pointlessly gross), bloodshot eyes, dirty fingernails, toilet paper fragments anywhere, flies, white (non-jizz) discharge from pussies, excessive cellulite, varicose veins (in legs or tits), and I guess that's about all....
Oh, and if it's a straight porn film/vid, then I am not interested in seeing the guy's hairy asscrack/hole or his ugly mug as he's nutting (or pretending to). Actually, I'm not interested in seeing much of the guy at all, except for maybe what his hands are doing and what his cock is doing. Watching a cock blow jizz can be arousing because, of course, I imagine that it is MY cock cumming all over her...