Writing sex scenes can certainly be a challenge. A good scene will entertain your reader, maybe get their pulse up a little, and if you’re very lucky will get savored by horny teenagers like pages 54-56 of the Lolita they have to struggle through for English.
Done badly, sex scenes will turn your readers off faster than a mash-mix of pale hairy, C-grade actor’s asses.

On the same premise that knowing what crocodiles and flamethrowers look like keeps you alive longer, here’s a list of words that should be kept out of your sex scenes. Examples – actual, pulled-from-the-depths-of-erotica examples follow in italics.

To keep this article reasonably SFW, some naughty words have been censored.

1.Turgid
Over-used. Awkward. So over-used, in fact, that the actual definition has been shifted slightly in the vernacular. The single salvation of turgid is that it’s so closely associated with ‘wang’ that you can drop it into a clean, grandma-friendly ‘love’ scene and not offend anyone.
Helen looked down and gasped.
“But Chris! It’s so…”
“Turgid, my dear?”

2.Puffy
Ew. Engorged? If you insist. Swollen? Sure, it has a sort of naughty-clinical feel about it. Puffy? Puh-lease. Trying to type this freakish word makes my fingers shudder in revulsion. Unless you’ve been whacking your ‘durty bits’ around with the force and subtlety of ping-pong rackets, save puffy for describing black eyes.
The poor lady’s [magnolia] lips were puffy now from all that pumping action of the Doctor’s [table] and fingers and fist and arm.

3.Pound
So, you can all see what the issue is here. Now, don’t get me wrong – sometimes, we all need a good pounding. It’s great for a mid-range abdominal and cardio workout, it’s fun to ‘let go’ every now and then, and there’s a certain raw animalism that’s very satisfying for both partners.
That said, there is a certain brutishness about the word that advises strict caution in its’ use.
He pounded my mouth just the way he had pounded my [Chevrolet].

4.Buffet (Either to smite or eat)
This one isn’t a ‘Thou-Shalt-Not-Use’ so much as a ‘I’d-Really-Rather-You-Didn’t.’ Hey, gotta save my hyperbole for the ones that matter. This is still an awkward, ugly word, though. Now, we’re all a fan of the munchtastic branch of sex, but there are more elegant ways of phrasing than buffet. You can leave your all-you-can-eat jokes in the first draft, thanks very much. 
Unless your sex scene has a resounding amount of flatulence, you might want to leave the wind-driven buffet on the sidelines too.
The buffet really began as he tongued it out of her in one big curl and swallowed the cream and chocolate covered berry down.

5.Funnel
Now we’re getting into the ‘What? Who puts that there?’ category. If you think that you’re safe from a Funnel-ing, think again. Often, the only warning you’ll get will be a ‘love’ and an innocuous-seeming hyphen. Then it hits you, right in the cerebrum! Ka-Pow!
[...] slowly inserted the tip of the empty funnel into her wet and stretched out [bank statement].

6.Gash
Ugly, ugly word.
He had his [iPhone] buried deep inside her dripping gash.

7.Sheath
Sheath is one of those unfortunate synonyms. It’s found lurking in the pages of Harlequin romances read mostly by grandmothers, slightly overweight call center employees, and lonely CEO’s. If you find yourself accidentally leaning towards the word, stop. Consider. Plot. Reach for a thesaurus. If you use sheath, people will laugh at you.
It’s also usually indicative of weak, adverb-heavy writing.
Alexia seemed to have fainted with pleasure; her [deckchair] muscles squeezed my [cushion] length into her tight sheath, trying to extract every drop of [pinot] that was spurting inside her loving furrow. 

8.Plague
Yeah, OK. Probably don’t want to be talking about the Plague during your sex scene. People have sex during plagues, of course, all the time in fact. It’s practically an aphrodisiac. But it doesn’t tend to run through conversations or internal monologues during sex.
Tends to put one off one’s stride a little.
Simone yelled, “[Insinuate] me! [Admonish] me like the Plague [acknowledged] my parents!”

9.Pustule
This is the last time I take reader suggestions for my articles. Yes, Pustule is a word you shouldn’t use in your sex scenes. If you have a character with an unfortunate disease, probably don’t harp on and on about it.
Interestingly, people with pustules do have sex. Sex in real life is often awkward, ugly, clumsy, sweaty, and smelly. Mushing bodies together makes weird and occasionally hilarious noises. So don’t be afraid to show that side of it as well.
Pustule pustule pustule pustule moan shudder pustule pustule.

10.Tsunami
Occasionally found as a synonym for what less imaginative writers would use ‘gush’, ‘wave’ or ‘torrent’ for. Hyperbole at its finest, but given a recent spate of Tsunami disasters, it might be more sensitive to use a different word.
First a tsunami of cream flooded her [fridge] and then Allan’s [mayonnaise] leaked into her [sofa].

11.Odor
Is there any reason you can’t use the word smell? 
No, I didn’t think so. Don’t use odor unless you’re over 80 and are referring to something dropped on your garden by a small and offensive dog.
Jim stepped into the room and could smell the odor of excited [hammock] from the six [diligent] girls.

12.Antidisestablishmentarianism
Philosophical arguments in general are best kept out of sex scenes.
“I’m not going to let you [clarify] my [blink]ing [headlights],” Sandy whispered throatily, “until we agree on antidisestablishmentarianism”.

13.Salami
Worst. Similie. Ever.
Ew.
[...] forced my mouth open and stuffed his hard salami down my throat.

14.Cactus
Perhaps I wrote too soon. Kinky is when you use a cucumber. Cacti qualify as a fetish. Don’t use it as a simile, please, unless it’s hard, dry, waxy and spiky. 
On reflection, not even then.
He said, “Now you’ll find out what a real cactus can do.”

15.Hoe-down
You might think it’s funny, but it’s not. None of the possible ways you were thinking of using this word are in any way, shape or style remotely hilarious.
He mewed with delight and proceeded to hoe down on her [bookmark].

16.Throbbing
See Sheath, Turgid. Over-used, under-loved, can’t take it seriously.
For fun and profit, try using it in normal conversation and writing, though.
I could feel his hard [toaster] throbbing against my [surfboard].

17.Fornication
Settle down there, Preacher Man. Get thee to a thesaurus! Fornication’s one of those words that’s only used because it exists: there are better words for every circumstance, but people occasionally revert to this one out of bewilderment. Know your language better than that, and pick the right word for ‘doing the deed’.
Fun Fact: Fornication has been with us since the 1300′s, deriving from Latin, fornicari.
Come, I will show you the judgment of the great harlot who sits on many waters,with whom the kings of the earth committed fornication, and the inhabitants of the earth were made drunk with the wine of her fornication. – Revelation 17:4

Phew!
So there you have it. Now that you’ve safely removed those words from your sex scene, you can rest assured it’s practically perfect.
With these lessons in mind, remember the three “R’s”:
wRite +
Revise =
eRotic!

And to make up for that awkwardness, here’s a bonus section:

Horrible Synonyms for Sex I Came Across (Heh Heh) While Researching This Article
Doing the Rump-Shaker
Interior Decorating
Popping it in the Toaster
Spearing the Bearded Clam
Skroging (What does this even MEAN?)
Dance the Blanket Hornpipe
Have your Banana Peeled
Bang like a Shithouse Door
Dash up the Channel

Until next time…

Go write!