These are in no particular order.
1) Receiving anal sex from a lumberjack wearing a torn flannel shirt, in a cabin, when he is sweaty after having just chopped down a tree.
2) Giving a blowjob to a musclebound cop to get out of a ticket.
3) Prison sex. (Not prison rape. Well...it starts off menacing. My cellmate is wearing an orange jumpsuit, the top tied around his waist, wearing a ribbed wifebeater. On my first day, he alludes that I'm going to be his "wife" and that he's going to "have fun with me." Later, though, another inmate starts to fuck with me and I beat him with a chair so badly he has to spend a few weeks in the infirmary. After a week in solitary, in my first night actually in my cell, my cellmate pins me against the wall, asks me if I feel tough, if I think I won't need him for the next couple years I'm in the slam. He leans in close, presses his muscles against me, and tells me that as strong as I am, he's still stronger. He places my hand on his giant cock...well you know where it's going.)
4) Werewolf sex. I don't really know the specifics of that one. But damn Alcide turns me on.
5) Military sex. Preferably with a buff Marine, wearing his dogtags with his camo pants around his ankles.
6) Sex, in formal wear, in a cramped coat closet at some sort of party, ball, or gala event.