Good topic, actually.
I'm not into rape or anything like that AT ALL, but I do like it when there's a bit of candid friction between the performers, rather than both of them zoning out for 20 minutes.
I remember a scene with Brooke Banner (whose bitchy attitude sets her apart from the crowd of dazed teen wreckage IMO) and Lexington Steele where he blasts her twice, both times with no notice (which was awesome), and at the end she whines that he's "a bad warner" -- that he didn't give her the professional courtesy of letting her know he was about to cum, so that she'd be ready and in the right position, etc. Instead she got blasted by surprise twice from point-blank range.
I do recall a great amateur video -- probably husband/wife -- where after a minute or so of gentle thrusts, he starts giving it to her doggystyle in DEEP... HARD... DELIBERATE... THRUSTS... that made even her modest C-cups clang together and her hair go askew. She turns back and gives him this look as if to say "you're not playing nice" and he knowingly THRUSTS into her again, making her head snap forward and her hair go everywhere. Then she looks straight ahead at the camera and whispers, "you're..." he POUNDS against her buttcheeks "an... ASSHOLE..." he POUNDS her again, sending her tits surging forward... "ASSHOLE!" He was obviously showing off for the camera, and she was obviously telling him that he'd PAY for it, SOMEDAY, SOMEWHERE. What goes around, comes around, hubbie.
