Vanity Is Feminine
The notion that vanity (in the specific sense of being preoccupied with one's physical attractiveness and desirability to others) and femininity are intrinsically linked: to be feminine is to be vain and to be vain is to be feminine. A woman who is not vain (and preoccupied with how beautiful others perceive her as) is not fully feminine, either a tomboy or immature (or both). A man who is vain is not fully masculine, quite possibly a weakling or homosexual. Handsome men are often described as "ruggedly good-looking," emphasizing their lack of attention to presentation.
This trope tends to be comedic, though it has its darker side. Women will pack a week's worth of clothing for an overnight trip. They will primp and preen in front of any shiny surface they happen past. They are ridiculously vulnerable to flattery and even the most level-headed types will turn into a Horrible Judge of Character if Nasty McVillainstein pays them a compliment based on their physical appearance or choice of dress. They will also be tempted, far more than their male counterparts, by promises of youth and beauty at whatever cost. There's a reason the Vain Sorceress is an almost exclusively female character type.
Usually this is presented as a weakness, an in-born proclivity to sin that virtuous women should strive to overcome. However, in other cases it is used to demonstrate ostensibly positive growth. A shy girl who starts primping and preening might be said to have "come out of her shell". A tomboyish child who suddenly starts caring about high heels and lipstick will be "growing up". In such a narrative, it is the woman who shuns vanity that is said to unnatural and shrewish, scorned and despised by the opposite sex.
All of this is flagged as a pure gender role. Women are not vain due to their individual personalities but their very sex—one vain woman in a cast of many modest ones does not fulfill the trope. One non-vain woman in a cast of many conceited ones does, especially if she's viewed as odd (either unnatural or virtuous, depending on the attitude the narrative takes).
The implications of this trope tend to be even nastier when applied to men, as the implied femininity is a grievous insult. The audience may get a chuckle out of the sight of a manly man checking his hair in a store window, but a consistently and overtly vain man is a subject of ridicule and disdain. They will be foppish, cowardly, quite possibly gay in a narrative which makes clear this is a negative and undesirable thing. The Sissy Villain owes much to this trope.
The more indulgent version of this trope is often paired up with All Men Are Perverts, by way of balancing out the genders' respective weaknesses. All women want to be looked at, and all men want to look. Works that believe in the Mars and Venus Gender Contrast are especially likely to make use of it. It is the polar opposite to the concept of metrosexuality, and has waned in recent times as mores change and gender stereotypes are discarded, but not yet a Dead Horse Trope. Contrast Real Women Never Wear Dresses, and Agent Peacock, a Bishounen badass whose vanity will not detract from their worth and respectability. The Sharp-Dressed Man may or may not fall peril to this trope, depending on how personally he takes his reception, rather than viewing it through a purely detached perspective.
- A Ranma ½ installment had Kasumi confront Ranma after he'd once again insulted Akane on her appearance, saying he needed to apologize and cheer her up. When he needs to know why, she replies that while Akane may be stubborn, awkward and tomboyish... "she's still a girl."
- Heck Ranma himself is an excellent example. Though he believes himself handsome in either form, insulting his looks as a man will merely annoy him. Insulting his looks as a woman will send him into an absolute berserker rage.
- In the Sonic the Hedgehog issue where Sally cuts her hair and coyly asks Sonic if he likes it, he responds that he'd never known her to be "so... girly." (Ironically this was intended as a sign of her de-Chickification, which had had her mooning and crying and generally being passive and ineffective.)
- Troop Beverly Hills uses this comedically and positively. Phyllis and all her girls are vain, and are able to charm a female judge by complimenting her. When Annie does her Heel Face Turn, it is accompanied by a new and more flattering wardrobe. The villainess Velda is plain, mannish, and cruel, plainly uncomfortable the one and only time she's seen in a very conservative dress. She is portrayed as a bad mother (who doesn't even like to be addressed as such), and her unattractiveness is made fun of.
"Or we could leave her here... to be toyed with by lonely mountain men. [Glances at Velda.] Really lonely mountain men."
- Used humorously in 10 Things I Hate About You when feared bad-boy Patrick is told Katerina prefers "pretty guys."
Are you telling me I'm not a pretty guy?
- The nastier version comes into play with male model Joey, a Jerk Jock who winds up getting his comeuppance via a thrashing from the petite Bianca.
- Dr. Frank N. Furter from the Rocky Horror Picture Show. He's extremely vain and does have a feminine (if rather harsh and demanding) personality to him.
Whatever happened to Fay Wray?
That delicate, satin-draped frame?
As it clung to her thigh
How I started to cry
`cause I wanted to be dressed just the same.
- The Wheel of Time. Some women are more inclined to it than others, but this always bears out as a cultural thing, where some societies encourage or discourage such behavior. A great deal is made of female hypocrisy as the characters look down on women who blatantly play up to male desire, but ultimately they all do it, deliberately embracing it after circumstance or jealousy drives them to it initially. This is seen as the natural and correct state of the world, as women who don't cater to male attention are even more underhanded and often outright villainous.
- The Narnia books have a fair amount of this. The otherwise completely down to earth Polly immediately starts to trust Diggory's Obviously Evil uncle after he calls her pretty. Lucy, generally shown as more virtuous than her older and vainer sister Susan (who was disgraced from the heroes after she grew up and took too much of an interest in lipstick and nylons), is so tempted by the idea of being more beautiful and desirable than her that only the appearance of Aslan stops her from casting a spell allowing her to do so.
- Xanth is another fantasy series that caters to this concept, taking the All Women Are Vain and All Men Are Perverts approach. Xanth's archaic prohibition against female rulers is presented as unfairly sexist, but the concept that all women desire to be considered beautiful more than almost anything else, and enjoy being seen as beautiful more than the promise of privacy, is completely inoffensive and simple truth.
A pretty girl could express shock and distress if someone saw her bare torso, but privately she would be pleased if the reaction were favorable.
- Gilderoy Lockhart of Harry Potter and the Chamber of Secrets. His pride may have made him a villain, but it is his vanity that makes him unlikeable in the first place, and he's mocked for it throughout. He eventually proves to be a lying, ineffectual coward whose triumphs are a scam. Also, the guy dresses like this.
- Admittedly, his vanity wasn't disliked because it was feminine, but because he could hardly go a sentence without saying how great his smile was. The majority of the major female characters in the books don't seem to care too much about their looks, except on special occasions, like balls and weddings.
- The Belgariad makes some use of this as well. Certainly no female is established as neglecting her physical appearance when she had any other option available. While 7000-year-old Belgarath appears as an old man (and in fact takes care to look like a vagabond), his 3000-year-old daughter Polgara appears eternally 20—by choice, since while an elderly male sorcerer may appear learned and formidable an elderly female sorceress would be seen as a crone. Though as a child she kept herself filthy and unkempt, after her sister's marriage she came out of her shell and went to the opposite extreme entirely, constantly bathing, preening, and dressing flatteringly.
- The hosts of What Not to Wear take clients (mostly female), who don't wear flattering clothes or apply makeup and then do their very best to assert that this lack of vanity is due to some very serious psychological issues and that the only cure is to make them dress up 24/7. Men are given the treatment too, but without the psychological aspect. Men not caring about their appearance is just slovenly. Women not caring is a denial of their very gender.
- Queer Eye For The Straight Guy seems to be built around this. Straight, "masculine" men are not expected to know about matters of style and taste, but gay men can be their tutors.
- Played with in Frasier, where not only Frasier and Niles' excessive vanity about their clothes and grooming, but simply the fact that they have good taste and style, is seen as effeminate and therefore undesirable. This is despite the fact that they always look good because of this—oh no, men are supposed to just accidentally throw on random clothes that they happen to look dashing in.
- In Star Trek TOS, all of the female characters were very pretty, and Uhura was by far the most vain of the main cast. When they were all tempted into staying behind on a land run by robots, Spock was offered great knowledge and opportunity for learning, McCoy was offered great medical facilities, Chekov was offered beautiful robot women to obey his every command, and Uhura was offered eternal youth. Even more obviously, in And The Children Shall Lead the characters' worst fears were shown: Kirk's was losing command, Sulu's was facing certain death that he had to maneuver the ship out of, and Uhura's was...being old and ugly.
- Shania Twain's song "That Don't Impress Me Much".
I never knew a guy who carried a mirror in his pocket
And a comb up his sleeve - just in case
And all that extra hold gel in your hair oughta lock it
'Cause Heaven forbid it should fall outta place
- Katy Perry's "You're So Gay":
I can't believe I fell in love With someone that wears more make up and...
Cue the chorus: You're so gay and you don't even like boys.
- Paranoia adventure "Send in the Clones". The Teela O'Malley clones in the final battle are dangerous opponents. However, they can be neutralized just by giving them a small mirror, which causes them to primp and fuss with their hair and check their eyeliner and complexion.
- Avatar: The Last Airbender: Even Toph, who was thrilled to learn the actor playing her was a huge bulking male, hides a side that wants to be pretty, was deeply hurt by girls mocking her appearance, and shared a bonding experience with Katara as they went to a beauty spa.
- The Smurfs: Vanity Smurf would seem to fit the bill, a narcissist never seen without a mirror at hand. Naturally, he is quite Ambiguously Gay.
- A Hey Arnold! episode plays around with this when the girls throw a makeover party and deliberately exclude the tomboyish Helga. When Helga tries to play with the boys instead, they mock her for being ugly and unfeminine. Helga caves and dolls herself up, then joins the other girls at the party. After a while, she starts to realize how ridiculous the whole thing is, considering their age. "We're nine years old! We don't have signs of aging!" She persuades the other girls to her side... and they wind up administering the intended makeover to one of the unfortunate boys who tried to crash their party and found himself outmatched.