Writing Sex Scenes (and: worst and best sex scenes?)

NOTE: IF UNDER 18 OR EASILY OFFENDED, DON'T READ ANY OF THIS. REPEAT: GO. AWAY. NOW.Might as well resign myself to the fact I'm going to be working on Finch 24-7 and taking little breaks, so I will be touching base here from time to time as warranted...I've been thinking about sex scenes because Finch has two such scenes, both explicit. They're important because they help define the relationship between two characters.But the fact is, writing sex scenes is a little like writing about characters having lunch--not inherently dramatic. You could say that this is true of any kind of scene, but sex scenes have an additional danger: they have the potential to throw off the balance of the story or novel because the reader's interest in and reaction to them is disproportionate to their importance in the context of the narrative.Whether you're writing an explicit or more subtle sex scene, you first need to make sure you have a reason for including it. Then it's best to keep six things in mind:(1) Get the choreography right. Basically, you can't have someone on their stomach in one sentence and then on their back in the very next sentence unless the reader gets some transitional clue. You can't have bodies interacting in ways where you can't clearly understand the ebb and flow of the physical acts occurring. So, in a sense, like any scene, you have to have at least a rough idea of sequencing. Otherwise, unintentionally laughable effects are bound to occur. Keep in mind, too, that in the context of a sex scene the choreography is always going to tell the reader something about the relationship between the participants. Stilted, awkward sex is certainly a tell of some kind. Playfulness is another indicator.(2) Get the physicality right. Um, sex is a very physical act, engaging all five senses. You don't want to overdo that aspect, but if you don't include that physical element, your scene is going to read like two stick figures are getting it on.(3) Don't use offensive or stupid terms. Several words leap to mind that are either offensive or stupid in the context of a sex scene. You should know what they are, and I'm not going to repeat them here. Just be aware of your terminology, because if you make a mistake or use something inappropriate to the context, your sex scene will either turn people off or annoy them. Terminology should not bring the reader out of the story.(4) Beware of metaphor and simile. I would suggest using metaphor and simile sparingly in sex scenes. Such devices can get you into even more trouble than inappropriate terminology. Use of comparisons to avoid being explicit or to add drama can land you in much more trouble, and contribute to appearing on the laughed-at end of the sex writing spectrum.(5) Don't use web pornography as your research. Received ideas are generally bad. Received sex in our increasingly porn-centric world isn't the kind of research you want invading your scene. As ever, you are looking to portray individual, specific moments that pertain to the specific characters you've created at a particular time in their lives. (Also remember that web pornography tends to be male-dominated and increasingly reflects male power trips, which also limits its usefulness to your story or novel.)(6) Keep it brief. I have to go back to the meal analogy, no matter how much giggling I hear from the peanut gallery. Would you show a character eating a meal over five or six pages? Probably not. Keeping sex scenes brief tends to get rid of a certain repetition that sets in--a real snooze-fest, at least in fiction. Brevity also protects you against magnifying your mistakes. If writing sex scenes is not your thing but you have to attempt it, at least the reader will only have to endure four paragraphs of your catastrophe, not four pages.No rule about writing is written in stone, but I think these six points might be of use.What sex scenes in fiction have you found particularly good or particularly bad?