You would expect the people creating erotica to know how sex works, and yet, the movies often depict things that wouldn't really be enjoyable, should be done differently or are just plain weird. This is usually done on purpose, to conform to what the audience wants to be true. Some of these are perfectly Acceptable Breaks from Reality, since such works caters to customers' sexual fantasies rather than reality and is intended to provide an arousing display of the participants rather than a strictly accurate depiction of the act.
In other words, Reality Is Unrealistic.
However, this also shows up in a lot of Fan Fic because said fiction tends to be written by teenagers who don't know all that much about sex. It can also be an effect of lack of research before writing about anatomy that the author lacks. Better to just use a Sexy Discretion Shot and call it a day.
Sadly, this trope sometimes pops up in works and speeches not clearly labelled as fiction: In Real Life, sex education fails YOU. The average high school sex ed course in many countries, especially the United States, is often so hilariously incomplete and inaccurate that it leaves you completely unsurprised that most students walk away knowing very little.
Compare with Idealized Sex, where the sex is realistic in action but still more idealized than most sex in the real world. See Miss Conception, Technical Virgin, and But We Used a Condom for when characters are mis- or uninformed about sex facts.
- Bigger Is Better in Bed (when sizes cross the fine line between "Wow!" and "I'm scared!")
- STD Immunity (well, biologically implausibly safe sex)
- Right Through His Pants
- Mr. Seahorse (men getting pregnant)
Common versions (no specific examples needed):The common versions can be divided into three broad categories: exaggerations of reality, convenience tools, and completely impossible.
ConvenienceThese remove inconvenient bits of reality. Certain needs that actual sex would require, but would affect the pacing of the sex/story.
- Implausible lubrication or complete lack thereof. Saliva and plain water tend to dry too quickly. Oils can degrade latex. Other works use things that are sticky or tacky.
ExaggerationsThese are at least theoretically possible, but for them to happen in reality would require nigh-superhuman sexual capabilities and/or stamina. Also covers cases where they are very possible, but the frequency of their occurrence in the wild is exaggerated.
- Doing it twice (in five minutes): Men tend to need a cool down period.
- Excessive amounts of bodily fluid (a woman constantly gushing out at the bottom, not just people sweating): There's a limit to how much fluid the human body can produce before becoming dehydrated, which typically heralds the end of an encounter in real life.
- A virgin always bleeds: A very common and very old myth in real life, and thus it's no surprise that it turns up in many works of fiction as well, so prevalent that faking it is a trope in its own right. The reality is that some women's hymens bleed during sex and some don't, sometimes even if it's not the woman's first time, which is all totally normal.
- All women are born with hymens, and a virgin will always still have theirs. The hymen is not a piece of organic cling-wrap blocking the uterus. It is a thin layer of tissue inside the entrance to the vagina that is loosely donut-shaped like the rest of it, just happening to be susceptible to tearing and bleeding (which is not guaranteed), and being so close to the entrance means it can be torn by other means. Sex and even pregnancy with an intact hymen is uncommon, but absolutely possible, so the state of the hymen is not a reliable indicator. And yes, it's rare-but-possible to be born without a hymen.
- Inversely, a lot of pieces focusing on Their First Time or virginity as a fetish will neglect to mention any difficulties with the breaking of the hymen or bleeding or pain at all, or the woman in question is having so much fun she just gets over it without even taking a breather. Realistically, pain in such a tender spot can be a real show-stopper.
- Female orgasm from penetration alone.
- The Elusive Orgasm: Since the 1990's, it's become a fairly common sex joke in comedies (film, television, whatever the case may be) that a male partner in sex has extreme difficulty giving his female partner an orgasm.
- All gay sex is anal.
- Sperm as guided missiles: Typically in fiction, if a couple have unprotected sex, the woman is absolutely guaranteed to become pregnant. It doesn't work like this in real life, as anyone who knows people trying for a baby can probably guess. This is only if the pregnancy can be used for drama, though. Otherwise, you can and probably will have a million James Bond-type characters who go around having rampant sex with the Girl of the Week and never have to face a consequence.
- Nothing smells, tastes bad, or is uncomfortable: Anything that would in Real Life is glossed over.
- Everyone enjoys the same things: It's as true with sex as it is when it comes to pizza toppings.
- Feeling heat in the belly after ejaculation: This experience is different for everyone. Some feel it and like it, some hate it or don't feel it at all. Naturally this variance is ignored in fiction.
- The vagina stretching to fit a huge penis: if the stretching from the dick alone approaches the realm of Balloon Belly, then it poses an immediate danger to the pelvis, leg joints, and internal organs.
- The vagina not visibly stretching to fit a huge penis: Unless the guy's poor manhood is getting painfully crushed, this is simply not physically possible and is equivalent to thinking the dick plunges into a Pocket Dimension.
Plain impossibleThese are not physically or anatomically possible by any stretch. They represent imaginative fetishes at best, or just severe cases of not knowing how human bodies work at the worst.
- Weird anatomy: Occasionally seen in hentai, and really common in fanfics written by virgins. This generally involves misplacing body parts or making them connect, stretch, or move in ways impossible in real life. Sometimes done on purpose in Sci-Fi and Fantasy but otherwise generally a sign of either Artistic License or lack of research.
- Mistaken terminology: Many writers don't actually know what names correspond to which body parts. This can lead to weird anatomy as mentioned above. Most of it is a result of badly done sex education classes which result in writers not knowing the proper terms or assuming that everything down there is the same thing.
- Bizarre comparisons: A staple of Purple Prose, this most likely is done for either romantic or erotic reasons.
- Implausible positions: Many of these would dislocate some joints if performed in real life.
- "Go fuck yourself!": The euphemism turned literal.