I know I'm said this before, but I will say it again and again because it's true. Writing sex scenes, especially hot sex scenes, is a lot of times one of the hardest, most awkward things I do. Why? Because you have to keep track of clothes, body parts, positions, what the characters are doing, and try to simultaneously picture it, write it down, make it sexy, and not be distracted by what's going on in your head all at the same time.
Trust me, not easy, but it can be done.
I guess that's why it annoys me when I'm reading a sex scenes, picturing it in my head, and the author mentions the character doing something that it anatomically impossible. It's very jarring. Here are examples of the latest two problems that are annoying me. I'm going to need some help from two characters, Adam and Steve, in order to explain. Not that these problems don't also happen sex scenes between a man and a woman or between two women, just that I feel like using two guys in my examples.
Example 1: Anatomy is your friend
Adam and Steve get on the bed until they are laying face to face, arms wrapped around each other. Chest to chest. Their tongues entwine as they kiss. Steve kissed along Adam's jaw line, kissed the nape of Adam's neck, and then returned to Adam's sweet lips.
Woah. Back up. Steve kissed the nape of Adam's neck? People are obviously confused as to where the nape of the neck is. Wikipedia has an article on the nape. It is the back of your neck, extending from the hairline to about even with your shoulder blades. Unless Steve's own neck has become extra long and extra flexible, these two are not chest to chest, arms wrapped around each other, and kissing napes. The human body does not work that way.
Not that this is the only example I see, but you get the point. At the very least please use the correct term for the correct body part. Otherwise you get a man poking a woman's uterine wall with his penis, or other such nonsense, and your readers will point and laugh at you. A lot.
Example 2: I can tell you have never actually been in a position to try that
Adam fell onto the bed. The mattress was soft under his back. Steve laid down on top of him, pressing him down with his weight. They began to kiss slowly, until Steve ran his nails down Adam's spine. Adam tried to arch into Steve, but couldn't because of his weight upon him.
Wait. If Adam is pressed down into the mattress, on his back, how the heck did Steve manage to work his arm up under him to run his nails down Adam's spine? I'm not saying it's not anatomically possible. I'm saying that it would be really, really difficult with a mattress in the way. I read stuff like the above, and all I can think is "There is a person who has never tried that in real life."
And now, I shall actually attempt to write rather than complaining about other people's writing. The end.