In Real Life this is common enough among Japanese girls that weekly or monthly shojo manga publications more likely than not include breast enlargement ads, or at least diet ads that promise to not take anything off the rack. Aside from the usual before-after photos, exciting exclamations and shiny products, there are specific ad mangas: 8 to 12 pages of A-Cup Angst and Buxom Is Better played straight enough to put a ruler to shame with no other content.
Ad for Chasteberry E: Meet miss Pettanko. Her life sucks. The boys don't even know she exists. She attempts to ask her crush out, he awkwardly evades. She knows the solution is to develop breasts. Cue desperate attempts, and finally success when a friend tips her off about the product. 3 months later she has gone from zero to cup E or so, attracts the Male Gaze wherever she goes, and is happily together with her crush.
Louise from The Familiar of Zero. Saito has said there was "nothing" there, and considering almost every other female (especially Tiffania) in the show is extremely busty, Louise really gets aggravated over this. Violently aggravated. In episode 2 of the third series, Louise goes into an over-the-top extended rant denouncing large breasts. Except that immediately after coercing Saito, her Love Interest, into declaring his preference for small breasts over large ones, he is caught in a compromising position with Tabitha, who is even flatter than Louise. Resulting in a new insecurity for Louise, and of course more pain for Saito.
It is revealed that pure-blooded elves are naturally flat-chested. Luctiana gets slightly jealous of Tiffania for inheriting Gag Boobs from her human father's side of the family.
Iori Minase The Idolmaster. The recent anime adaptation gives her an episode where she tries competing with Azusa by padding her chest literally WITH MELONS.
Nanoha of Eensy Weensy Monster. Her boyfriend Hazuki was shocked to the point of dropping something when one of her friends made an offhand comment about "them".
Mazinger Angels: Sayaka and Hikaru find themselves wanting compared with Jun. In one scene, they are having a shower, and Jun gets nervous because they are staring at her very focusedly. Then they look over themselves and sigh in resignation.
The OVA gives Princess Ayeka a little of this when she realizes that Sasami will grow up to look like Tsunami, the Goddess of their race.
Her arch-rival Ryoko also rarely misses a chance to tease Ayeka about her breast size. Which is not, in fact, small. It's just that nearly every other adult female in the series has very noticeably larger breasts.Especially her own mother, Misaki.
Filler Rukia is afflicted with this. In the Bount Arc, she's enraged when Kon compares her to a wall. In the Rock Musical, she shouts at Yoruichi about breast size being unimportant. In Bleach: The 3rd Phantom, she feels left out when Rangiku and Orihime compare breast sizes. Canon Rukia doesn't care at all.
Hiyori was annoyed when Mayuri called her a boy upon their first meeting and shouts that she will show him her breasts to prove her gender.
Shino gets very upset when she heard others saying that she hasn't developed breasts of her own.
Sera in Detective Conan is a milder example. She has small breasts and even gets mistaken for a boy on a regular basis, but she mostly just shrugs it off aside of a few comments. ("They're due to pop out one of these days...")
Kyoko from Eiken is the "other" lolicon character in the series who looks much younger than her 15 years, and so has no breasts or curves to speak of. In a club, let alone a world, were a D-cup is considered small, and most of her clubmates have bigger boobs than their heads, she pines for a voluptous body every time she "thinks" she's alone. It is implied, however, that she isn't short so much as a very, very, very late bloomer and she will eventually grow up to look like her mom (who compared to the other girls is still quite small).
Heavy Metal L Gaim: In episode 9, Amu notes that Leccee's breasts are bigger than hers and gets jealous.
While she's probably better endowed than almost everyone else on this page, Lina has had the bad luck of accumulating lots of overly busty female allies. Plus the youngest of the group, Amelia, already outmeasures her and is still filling out. So she thinks she's flatter than she actually is... and if you tease her about it, she's liable to blow up your entire village with you as Ground Zero. In at least a few of the earlier OVA's she drawn very flat, but does grow with the series to having at least some sort of chest. The artists seem to note that Lina really didn't have much to complain about in earlier season and decided to draw her flatter later... giving off the impression that her breasts SHRUNK as she got older.
The "Extra Edition" OVA of Sword Art Online shows Silica feeling somewhat down about the fact that her other female friends (particularly Suguha and Lizbeth]] have more generous busts than herself.
Natsumi Murakami seems older, although slightly built herself, and displays the insecurity far more blatantly. It does not help that she is rooming with Ayaka and Chizuru, two of her most... maternal... classmates.
Pachira from Magical Pokaan once (secretly) mail-ordered a bust-enhancing machine, with minimal results. The machine was the real thing and was working fine, but Pachira had to return it before she could get more visible results, which made her Pettanko status hurt even more.
Minami of Lucky Star, who is completely flat. Any tactics she used to combat this just ended up making her taller. She, Konata and Yutaka also released a joint Image Song album that collectively titled them the "Mune Pettan (Flat Chested) Girls". Really, her angsting on her boobs has gone to an Once per Episode frequency.
Mahoro longs for bigger breasts; it's an inferiority complex fueled by Suguru's fondness for porn and Ms. Shikijo's endless taunts. Since she's a combat android, her flat chest was probably just a practical design choice. In fact, to her chagrin, it's actually the deciding factor in one fight (she body-slams her opponent, shouting "Bitty booby attack!"). The Triomatic girls poke fun at Mahoro's small chest at one point in the end theme of season one.
We learn just how big a hangup this is for Mahoro in her All Just a Dream episode. She dreams of ordering an enlarging machine, only for it to work on everyone but her (including the male Suguru). The second half includes the notorious "OPPAI-MISSILE!◊" scene, which must be seen to be believed. The sheer amount of mental energy she puts into this makes you wonder if Suguru's grandfather has a point when he accuses Mahoro (she of the "dirty thoughts are bad" Catch Phrase) of having a mind just as dirty as everyone else.
The second-season end theme is all about chest size, but this time it's Minawa they're hassling, and they're a bit more subtle. ("If you worry about every little thing, you can't live your life"). Actually, Miyuki and Chizuko are in the same boat — Rin decidedly isn't, as she occasionally reminds them.
In an omake in the manga, Rin and Miyuki's rivalry to each other as Suguru's girlfriend become rather catty when Shikijo also tells them about Suguru's Buxom Is Better mindset, the fact that Chizuko, who usually stays out of it, also got into it says alot.
Chika Ogiue in Genshiken. In the Hot Springs Episode, Sue (who speaks almost entirely in anime quotes) pulls the "Status symbol!" gag while pointing at her, quoting Mayumi.
Hikaru, Umi and Fuu from Magic Knight Rayearth are like this, when the women from Cephiro take them for a bath, and found out that these women completely out-boobed them. But then again, they're 14 years old...
Tomo from Azumanga Daioh uses her lack of endowment relative to Sakaki to get a handicap when competing against her in a footrace, claiming that Sakaki had an eight centimeter advantage (Tomo still loses). Later on, Yomi mocks her size in a locker room scene, much to Tomo's anger. However, Tomo's definitely not the least endowed girl of the group (that distinction going to Osaka and, obviously, Chiyo-chan), just the one who gets jokes made about it (probably because Chiyo-chan is too young and Osaka too spaced out to care).
The eternal loli Vita of Lyrical Nanoha, who got the label of "flat chest" on an official sketch and has had her moments of snippiness in regards to breast size in the Sound Stages. Seriously, calling your leader a Boob Demon with a follow-up on how the size of a woman's breasts are inversely proportional to the size of her heart?
There's a De Motivator that shows her drinking milk while fantasizing about developing a voluptuous figure. "DREAMS. Everybody has them."
Like Lina Inverse above, Akane Tendō isn't really flat; she's actually well-proportioned for a 16 year-old. However, she has extremely deep insecurities about her bust size, especially when her sisters, her rivals and even her fiancé all make her look small by comparison (and he even flaunts it). Naturally, this is milked for all the humor possible. Those insecurities get even worse when Ranma asks her if she's gotten smaller. Cue Akane breaking out the magazines that show you how to "get a bigger bust through exercise."
UkyôKuonji isn't that much bigger then Akane. She avoids Pettankohood, however, because she doesn't really have any insecurities about her bust size. About her looks in general/attractiveness as a woman, yes, it's hinted (mainly in the anime) that she does have some worries in that department, but that's more because of being a Bifauxnen and thus worrying that Ranma won't see her as a woman.
Asu no Yoichi!'s Ayame. This is such a major part of her character that Yoichi was able to recognize that an impostor wasn't her simply because her breast size was too big. Naturally it's also a very sore spot for her, as her other sisters are quite well endowed. Made even worse when it turns out that she's even out-boobed by her youngest sister, Kagome, who's in elementary school. Yes. Notably, she's still decently endowed (Yoichi is able to get a substantial handhold) if she were in the real world. It's just that every other girl in that world is so large.
Yukari Sendo from Rosario + Vampire. Yes, she's only eleven (she's a Kid Genius, so she's in a class full of teenagers), but she does get teased about her flat chest quite a bit... and teases the highly busty Kurumu about her chest on occasion, as well. So, yeah, clearly she's insecure about being flat. In Season Two of both the manga and the anime she takes "grow older pills." Although still no Kurumu, she certainly will have nothing to worry about in a few years.
Nagi in Kannagi. She's well aware that Jin has a love of big breasts after finding his Porn Stash. When he joked that her chest had gotten bigger in one episode, Nagi said that if he spoke any further, she'd rip his ahoge off his head.
In the "Road to Ninja" tie-in manga, which has a bath scene, Sakura notices Hinata being her usual shy self and attempting to hide her body. She tries to reassure Hinata that since they're all girls, she needn't be that way. However, that wasn't necessarily the problem: Hinata's breasts are too big to stay in the water. Sakura's reaction to that is priceless.
There's also Karui. In her first appearance, she and Omoi argued over the possible reasons that they could have been called by the Raikage. Omoi thought he was going to be scolded for putting mayonnaise on his potatoes and for gaining weight; the argument started, however, with Omoi suggesting that Samui's back problems stem from her large breasts, which he mentions that Karui doesn't need to worry about. Karui gets pissed and responds by kicking him.
Fuu from Samurai Champloo is a bit insecure about her small breasts, especially when Mugen teases her about them, although it's implied that he does it because he likes her and doesn't want to admit it. In one episode, she poses for a nude painting and is flattered that the artist gave her a more impressive chest.
In Elemental Gelade, Cisqua is often teased by Kuea for her flat chest. Her fear of water is a mixture of being unable to swim and being unable to fill out a swimsuit. Even Cou teases Cisqua about it during a hot spring scene where he accidentally saw her topless. Plus in the anime, one of Cou's old friends calls Cisqua "bro" (despite the fact that she's wearing a dress), which causes her to flip out and attack.
Yuya from Samurai Deeper Kyo has a complex and gets teased quite a bit about this by the title character. She's actually very booby by "real life" standards.
Austria's genderbend also seems to be portrayed this way. In a webcomic on Pixiv, Austria and Liechtenstein are seen mourning about it. Also, one artist also on Pixiv drew her, Prussia, and Germany: with Germany at the big size (G Cup), Prussia at the middle size (E cup), and Austria as the small size (B cup). This is because Word of God said he applied A-Cup Angst to Liechtenstein because he saw that women in Switzerland and Austria ranked lower in breast size.
Japan's Nyotalia self is often portrayed this way too, especially since the canon sketches of her don't exactly emphasize her assets the way sketches of many other Nyotalia nations do. In one Pixiv fanart◊, she's shown weeping about having no chest compared to the extremely well-endowed Greece's.
Taiwan isn't as super flat as Liechtenstein, but she seems to be rather... troubled when she sees that the European females (save for Liechtenstein) are not only well-endowed, but not afraid to show it...
In Goshuushou-sama Ninomiya-kun Houjou Reika has small breasts and that gets particularly highlighted by Tsukimura Mayu's huge boobs. At one point, while wondering what's wrong with hers, Reika finds a solution worthy of a true ojou-sama: to make small breasts fashionable. The next episode's opening omake shows that through application of her huge wealth she has succeeded in making small breasts most desirable and big breasts a cause for humiliation; to the point that Mayu gets chased out of town for her breasts.
Maka from Soul Eater. Soul's nickname for her is "Tiny Tits". It never endswell for him. At around 13 Maka's young enough to grow out of this, and her concern about it. Being around a group of older rather well-endowed girls can't help, though.
Akina Nanamura in UFO Princess Valkyrie is flat chested and jealous of Valkyrie's breast size and is constantly harassed about it by her companion, Hydra, who also has large breasts (when she is not sealed away by Akina's Miko magic). Akina is once accidentally given bigger boobs in one episode. Rather than freak out like normal when caught up in such things, she's positively ecstatic!
Mikan Sakura from Gakuen Alice. At one chapter, Natsume had rubbed her chest before, commenting that it's not round, yet. Another example that when Mikan and her friends were eating candy to turn into older teenagers, Mikan appears with a flat chest (or at least that was what Natsume has stated).
Poor Meru has major issues both with speaking to other people out loud and with her flat chest. She compensates for the former through spiteful, abusive emails, and the latter with an inflatable bra, which blows up on first use.
Chiri has this as well. In one manga chapter, she comes to clean Nozomu's house, and wants to straighten things so there is less "dead space". Nozomu comments that she has her own dead space, wearing a bra that's too large for her. She responds that she uses the space effectively and pins him to the wall with knives. In another instance, Majiru is advised to inoculate himself against groping women later in life by doing so now, and is told to go for small breasts. He chooses Chiri and has a Color Failure when she turns her terrifying Game Face on him.
In Cyber Team in Akihabara we have Kamome, who at 13 is quite troubled for not being developed fast and big enough, to the point she regularly stuffs her bra. Meanwhile, we have Uzura, a Schoolgirl Lesbian who have an absolute passion for flat chested girls, to the point that she turns her attentions from Hibari to Kamome (and, in The Movie, towards Tsubame), as she realizes that each girl is flatter than the former. Kamome is not happy about having Uzura behind her because of the implications.
Kouyama Mitsuki in Full Moon o Sagashite is a pettanko to some extent. Well-endowed Meroko teases her for this in the beginning, brutally calling her "Puchipai" (puchi means tiny and pai means breasts) Mitsuki, as the teenage Full Moon blushes and says "I have breasts when I'm in THIS form!" When she turns back into a 12-year-old in the anime, Meroko again remarks that "her chest returned to normal" and Mitsuki asks her not to stare. Later on in the manga, Mitsuki develops a bit more after her 13th birthday but interestingly even as a true teenager (16) at the end, her chest does not look much bigger... (rather surprising for a main character from Arina Tanemura). Doujinshi artists also go out of their way to emphasize that Mitsuki is a indeed a loli character and quite DFC.
The heroine from Saitama Chainsaw Shoujo is a pettanko, despite having a partial American ancestry. "I wish I could have a body born of THAT DNA...!"
Kisara. It doesn't help that she's pretty much the only post-pubescent female in the cast without large breasts.
And while Kenichi's sister Honoka is a bit too young (13) to be worrying that she'll be flat forever, she is nonetheless self-conscious over it. Then again, if most of the girls you knew looked like Miu... She won't have to worry, her mom is pretty busty herself.
Hinagiku of Hayate the Combat Butler is often dismayed by this. Even though she rarely complains, Nagi is also concerned about it.
Seika of Princess Lover thinks she doesn't have a chance to win the guy. Considering her opponents I guess it's noticeable.
In the pilot episode, Ken tricks Kurimu (through Duck Season, Rabbit Season dialogue) into saying pettanko. After crying into her friend Chizuru's bigger chest for comfort, it only made her feel worse.
In the penultimate episode, Minatsu asks Kurimu, "President, where's the pettanko?" i.e. "Where's the flat (stamp)?" Trauma ensues.
In Crayon Shin Chan, a running gag is the constant competition on anything between two of the schoolteachers Midori Yoshinaga and Ume Matzuzaka. A running gag within the running gag is their cup size rivalry. For example, during a swimming class, laying down side by side on the floor and trading insults as to who was more like plains (as opposed to mountains).
Shin often makes jokes about his mom's flat chest. The Funimation dub has a running gag where she's saving up for a boob job.
Suzuna in Eyeshield 21. It doesn't help that the only other female character of note is Mamori who is...fuller up top. Nor does it help that she's the captain of Deimon's cheerleading squad, which is otherwise comprised of hot girls drafted from America (we never did find out how Hiruma arranged that...). During their first appearance the audience loved the show, but complained that "the captain's not sexy".
Sae in Hidamari Sketch. For example, when Yuno was discussing her arts program electives (2D-, 3D- or digital arts) with Hiro and Sae...
Yuno: Sae-san probably chose 2D? Hiro: Yup, she was 2D. She's clear about what she wants to do. Sae:(headdesk) ... Sae is 2D ...
Erutis from Demon Diary is quite flat-chested, and complains about it in an Omake which also includes a picture of her with an arrow pointing to her chest and the label "no bosom" (and one pointing at her legs: "stubby legs"). She says that this is the reason she was mistaken for a guy at first by many readers. The peculiar thing is that her chest doesn't really look all that flat; she's easily a B-cup. She just wears a baggy top.
The Movie also Plays with this. At one point Ranka is making a photoshoot for a construction company, wearing a swimsuit. The suit is modeled after the company, including its slogans. So, naturally, the phrase "Under development!" is written upon Ranka's left breast.
Kasumi/Misty from Pokémon, moreso in the manga than in the anime and moreso in the early anime episodes. She was teased for being "scrawny" and "looking like a boy" (often by Ash and often resulting in some impromptu abuse). In the manga, Ash even remarks that she could use an evolution stone to "evolve herself". This leads to a hot spring scene where the water supposedly promotes evolution, so she pours the water over her chest.... It should be noted this only applies to the anime. The games and most adaptations have her being rather well-endowed (though not on the level of other girls her age such as a few female protagonists), even as an eleven/twelve year old. She doesn't angst obviously, and is often called beautiful.
Ookami-san gives us both the title Ryoko Ookami as well as her best friend, Ringo Akai. Of course, they probably wouldn't be too concerned about it, if a certain Lemony Narrator didn't call frequent attention to the fact.
Inami-chan of WORKING!! is put out by her small chest, but it isn't that notable until Takanashi's crossdressing is larger than her that she begins to be bugged by it. Quite notably.
Marin and Moe of Brigadoon: Marin and Melan are both anxious about their nearly non-existent bosoms. (Given that they're in their first year of middle school, they have time to develop.)
In Steel Angel Kurumi, there is a variation where both Karinka and Kurumi are jealous of each other. Karinka wants to have big breasts like her sister, but Kurumi wishes hers were smaller (and she even mentions back pain which is common in real-life women with large breasts).
In Tegami Bachi, Niche, who hates milk, downs two mugs of tea because they have milk in them when the better-endowed Sylvette says that milk helps you grow up big and strong (or something like that). Niche, being a Maka, is weak to things that are hot. Like tea.
In one episode, Natsumi (who's about 14 years old) gets jealous of her mother Aki's breasts, even though Natsumi is no slouch in that department either.
Not to mention there's a whole episode revolving around Momoka (who's twelve) having issues about being petite. In Momoka's case, she's worried that since her crush Fuyuki is always surrounded by busty women like Natsumi and Aki, his standards for what counts as sexy must be very high.
In K-On!, when Ritsu sees Mio in her bikini, she really notices Mio's breasts... and hits her in the face with a beach ball. (The subject hasn't come up a lot so far, though.)
Artificial Human Ai from Video Girl Ai was supposed to be busty, but being played in Youta's broken VCR caused her breasts to shrink down to almost nothing. She becomes annoyed when she finds out about this.
In episode 12 of Nogizaka Haruka no Himitsu Purezza, Alice-chan had a moment of this. A ping-pong ball had got caught in Haruka's cleavage. When it was finally out, Alice picked up the ball and dropped it onto what would be her cleavage if she weren't a grade-schooler (or at least having the body of one). Her sigh and expression of disappointment when the ball just fell to the floor....
Inverted in One Piece. Kuina, Zoro's childhood rival, had angst for developing breasts at all, because it reminded her that she was becoming a woman.
Mikoto Misaka of A Certain Scientific Railgun is self-conscious of the fact that some of the younger students of Tokiwadai Academy have a bigger bust than she does.
Sayaka in Oku-sama wa Mahou Shoujo is teased about this, even when she transforms into an adult form. She's a little worried about it, but it mostly just appears when someone else brings it up negatively.
Nanael from Queen's Blade is essentially the only adult female in the world with normal-sized breasts, and it bothers the hell out of her. Especially once she has to room with a priestess whose breasts are almost the size of Nanael's body.
Wendy and Levy both suffer from this in Fairy Tail, though Wendy is more worried about being flat-chested when she's older, considering she's only 12.
Mavis is hinted to suffer it as well in a brief anime-only gag.
Dorohedoro has Ebisu, who is constantly trying to find way to enlarge her breasts, such as doing aerobic breast-enhancing exercises and stuffing things, even Kikurage, down her chest during the Blue Night. The dream mushroom En created shows Ebisu's desire having double D-sized chest.
Inverted and played straight in Yuru-Yuri. Sakurako is flat and jealous of the exceedingly busty Himawari. Himawari is self-conscious of her overdeveloped chest, feeling like it makes her stand out too much among their classmates.
Rinko of Omamori Himari has worries of this nature. Probably because three of her four rivals for Yuuto's affections are C-cup or above (the fourth is a loli).
Aoi of Beelzebub at times, mostly when up against her kinda-sorta love rival, Hilda.
Koma: Calm down. Whether they're massive or itty bitty, I love all tits. Aoi: ITTY BITTY!?
Shino of Seitokai Yakuindomo is very obviously jealous of her friend Aria's much larger breasts.
Yuko, Sorata's younger sister in Sakurasou no Pet na Kanojo, goes through this while groping Mashiro and Nanami's breasts in episode 7. Jin tries to cheer her up by yelling that she'll get bigger in high school.
In Kotoura-san, while Haruka's small breast was alluded to in episode 4 during Manabe and Zenzan's Ham-to-Ham Combat, this trope doesn't show up until episode 6's beach scene—and, especially, its ending.
Both female leads in Onegai Twins Miina and Karen have this.
You would also do well not to mention Elena's marked lack of assets.
The Pink Ogress, Tokiha Nadeshiko from Momogumi+Senki is extremely angry when ever someone called her Flat-chested(It should be noted that the other girls' breasts are rather average sized). For record, Tokiha doesn't even know what a brassiere is!
A very, very downplayed example, but Saya was clearly Blue with Shock in episode 6 of Servant × Service after Kenzou mentioned she doesn't have Lucy's... "stuff" that obstructs his view on the shoulder.
In Hataraku Maou-sama!, Emi Yusa is flat-chested and gets jealous of Chiho for having Gag Boobs despite being much younger than her. At times, Emi tries to claim that she's proud of her flat chest because it provides better mobility on the battlefield and because it means her armor is cheaper, but she is not fooling anybody.
In Binbougami ga!, Momiji is flat-chested despite being a goddess and hates it. It doesn't help that Ichiko makes fun of her because of that fact.
In Walkure Romanze, Lisa has some reservations about her own bust size especially due to the fact that the other girls have rather ample cleavage.
In Saki, Miharu Yoshitome, who's fairly flat-chested, is somewhat sensitive about being reminded about this fact while in the bath with Mako and Tomoki, the latter of whom has the second largest breasts of the prefectural finalists, after Nodoka. When Kaori comes in, Miharu indicates feeling the same way about her.
In in a manga omake for Achiga-hen, Shizuno is quite upset to see that her childhood friend Ako has not only grown significantly taller than her, but also has developed a larger pair of breasts, since starting middle school. Ako later tells Yuu after her semi-finals match that she wishes she had Yuu's luck and breast size.
Sophie Bangs in Alan Moore's Promethea is described by one of the past Prometheas as "flat-chested and neurotic," with the implication that that's what the typical candidate for Promethea-hood is like.
When Henry Bendix first recruits Jenny Sparks into (The Authority's predecessor) Stormwatch, she agrees on the condition that she doesn't have to wear spandex, saying "I don't have the chest for it." Most artist renditions since have been faithful to this concept. This did not hamper her sex life in the slightest, though living 80 years as an attractive 20-year-old who loves to party surely helped her there. Swift (being a typical Tibetan) was pretty flat-chested during Warren Ellis' run/ending on Stormwatch, but when the artists for The Authority drew her, she was given a much more substantial rack that got handwaved into being a "20-grand boob job."
Jubilee of the X-Men sometimes takes this role. In Generation X, which focused on the younger and less well-known of Xavier's students, her modest figure was used to contrast her against the model-esque Monet St. Croix. Sometimes Kitty Pryde takes this role, too. But much like Swift above, when Jubilee transitioned into the New Warriors relaunch, she lost her mutant powers, but gained two cup sizes in the bargain. (Granted, she was 13-14 for most of her comic history.) Entertainingly lampshaded◊ in Uncanny X-Men #268 — Jubilee is listening in to a conversation between Wolverine and the more commonly-endowed Psylocke and Black Widow. She glances up at the two women in their skintight costumes, peers down her vest to see how she matches up, and then drops her head in her hands with a frustrated expression.
Yelena Rossini from Transmetropolitan is just a bit touchy on the subject, which makes a certain amount of sense when you consider that she spends most of her time in close proximity to Channon.
Vanessa, a teenage supporting character in the old Wonder Woman comics, tended to bemoan her lack of breasts and was stated on one occasion to stuff her shirt.
Udda Von Schteppenslammer from Tank Vixens has "itty bitty mousie titties" and the members of the 101st battlion are so endowed.
Wilhelmina "Will" Vandom, the teenaged leader of the interdimensional Guardians, is quite explicit about it. She frets about her scrawny appearance, and prefers to be in her older, more tittacular Guardian body. As most of the art seems to show her arching her back◊ and sticking out her chest◊ in Guardian form, you can guess why. Actually if you look at the second picture there, she's clearly staring down at her enhanced breasts with excitement in the middle image!
Also Hay Lin to some degree. She too shows she likes her Guardian form. This is driven home in one episode: Cornelia's mother embarrasses her in front of the others by jokingly implying she stuffs her bra after seeing Hay Lin transformed and buxom, believing it's a Halloween costume with false breasts. Hay Lin suddenly looks angry and humiliated, and puffs up her chest some more to (over)compensate.
Ninjette's cheerily drunken confession to Empowered as to the reason she was in the employ of various thugs rather than a member of the Superhomeys summed this trope up (and unlike many artists, when Adam Warren invokes lack of the Most Common Superpower he does not use half-measures).
Ninjette: I can't be a goody-goody heroine 'cause I don't have a nice, big rack! *urrp* Can't be a good girl without a good set, right?
Assumptions: Though impossible for ponies to have breast sizes, the equivalent occurs where Rainbow Dash is rather sensitive about her "lack of curves." Along with her tomcoltish nature, this leads to very unflatteringassumptions.
Generally speaking, it's an enormously popular trend in Friendship is Magic humanized fanworks to portray Rainbow Dash as the most petite member of the main group. Although she's typically depicted as proud of her small breasts, given that Fluttershy (her best friend since childhood) is just as popularly depicted as being the most buxom of her friends, writers and artists love to hint that Dash is overcompensating to hide her insecurities.
Yet Again has Ghost announce an intro for fighters during the Chunin Exams. This comes up:
Ghost: "Let's get this started before we get any more distracted! Hyuuga Hinata AKA the only Konoha kunoichi that has hit puberty so far..."
Sakura and Ino: (look at Hinata then themselves and proceed to sulk in the corner) "I'm still pretty."
Films — Live-Action
Kitten Braden, the heroine of Breakfast on Pluto, although she prefers to call herself a "svelte gamine", as she indignantly informs the peep show customer who complains about her lack of endowment. Although in Kitten's case, this is only to be expected, since she's biologically male and not on any sort of hormone therapy.
In Elvira, Mistress of the Dark, one of the town residents, Patty, is this. She uses a variant of bra stuffing (falsies) to make herself seem otherwise, and keeps her small breasts a secret from the entire town... until The Reveal at the picnic!
In the medieval comedy Gladiatrix, the heroine's newly acquired French husband is disappointed over her lack of breasts. When she magically acquires breasts during the course of the movie, she's able to return home and tell her husband to carry out numerous household tasks.
They Call Me Bruce?: The title character comments on the fact that the nude woman sent to massage him has "breasts like a boy". She seems rather embarrassed by this.
Samantha "Sam" Baker from John Hughes' Sixteen Candles. According to his little brother, she's "only eating carrots to increase the size of her breasts." Sam later says about her bridesmaid dress: "I don't have one-tenth of the bod to fill the stupid bust up."
In the first Gidget movie, Sandra Dee is doing some sort of exercise to help pump her chest out.
Cameron Diaz's character in Bad Teacher suffers from this.
There's a mean-spirited joke that plays off this trope in Real Life:
"I just heard a joke so funny it'll knock you flat! (looking at chest) Oh, I see you've already heard it."
A woman is looking at herself in the mirror, sighing about her breasts being too small. Her husband overhears and says he has a solution. "What's that?" "Rub 'em with toilet paper!" "Toilet paper? How will that help?!" "Well, look at what it did to your ass..."
In The Princess Diaries, Princess Mia's biggest insecurity about her appearance is her extreme lack of a chest — it was pointed out several times by Lana that she doesn't even need a training bra. Granted, by the end of the series she has B-cups.
Based on a True Story, Catalina, the teenaged protagonist of the Colombian novel later international franchiseSin Tetas No Hay Paraiso, is a dark play on this trope. Catalina's real reason for wanting a bigger chest is to catch a rich boyfriend who'll buy her luxuries and get her out of her poor neighborhood, like the ones her bustier friends have. The catch is that those "rich boyfriends" are drug dealers and traffickers. She tries to approach that "rich world" by becoming a prostitute, but her beginnings are harder because most of her potential clients prefer chicks with "more meat". She eventually gets a bust augmentation from a Back-Alley Doctor and marries a minor boss of a Cartel, but she's still under her pettanko complex, by that point she has lost her True Love and any chance of escape, and eventually the brutal reality of the shady world she has gotten into hits her hard. When she is forced to reverse her boob job in a Life or Limb Decision, it's become the last straw for her, so she arranges a Suicide by Hitman to end her suffering.
Magrat Garlick has been described several times as being a physical match for an ironing board with two peas on top of it. Although being flat is not her defining characteristic in terms of attractiveness (the author also makes note of hair which refuses to cooperate) she certainly does seem to be very self-conscious of it. Now imagine how she must have felt in Wyrd Sisters when, having stuffed her bra among other preparations, she takes a quick survey of her assets upon encountering Verence and finds that her stuffing has descended approximately to her waist.
Lisbeth Salander in the first book in Stieg Larsson's Millennium series. Because of her flat chest and the fact that she's short and skinny, she is often mistaken for a 14-year-old. Her legal guardian even uses this fact to his advantage when he drugs and rapes her. He claims no one will believe he raped her since her small cup-size means she's not a turn-on (yeah, he's a jerk). In the second book though Lisbeth has gotten breast implants.
The Doctor's companion (later ex-companion and Adventurer Archaeologist) Bernice "Benny" Summerfield. One could probably draw quite a few conclusions about certain novel writers by counting up the number of times per book some of them have felt the need to mention her legendarily petite rack. Benny's creator, Paul Cornell, had a character describe her (in dialogue) as having "no tits".
Trix MacMillan, from the Eighth Doctor Adventures, is a less-prominent example, so to speak. Her breasts aren't big enough for her to have what you'd call cleavage. This only seems to bother her when she's feeling especially self-conscious, though. Also, she has some kind of sex-work-ish career in her Backstory, although that isn't necessarily saying a lot, at least in Real Life, and she manages to look glamorous and another character actually has nice things to say about her rack... but he Really Gets Around and has a 6'6" ex-girlfriend, so maybe he's not all that picky.
Jame in P.C. Hodgell's Chronicles of the Kencyrath is flat-chested and self-conscious about it. She's flat to the point of being mistaken for a boy all the time (being rather tomboyish doesn't help, of course). The master thief she's apprenticed to in the first book thinks she's a boy the whole time, even when she strips to the waist in front of him. After that, she gives up trying to tell him otherwise; granted, he's eccentric and has bad eyesight, but still. She also doesn't ever understand the crushes other characters have on her, convinced that there's nothing worth looking at in her. (One suspects she's rather blind to what she does have...)
In the fourth book of The Belgariad, Castle of Wizardry Princess Ce'Nedra has a suit of armor made for herself, and makes a point of trying to get a Breast Plate much larger than her actual chest. She settles for one just breasty enough that she won't be mistaken for a boy in armor.
In A Song of Ice and Fire, Brienne of Tarth, in addition to being riotously masculine all around, is flat to the point that she may as well not have breasts at all. Jaime once comments that she's like the Hound with teats — or would be, if she had any teats. She's not terribly concerned with her bust in general, but her flatness is part of the overall lack of femininity that often distresses her, as she is so often taunted and rejected for her appearance and knightly ambitions.
Averted in Michael Slade's Ghoul, in which Rika Hyde's flat chest doesn't stop her from playing up her onstage sexuality as a head-banging rock performer. Her lack of cleavage becomes plot-relevant when it gives away that a more buxom woman had impersonated her.
The main character in Michelle Cunnah's chick-lit debut "32AA" suffers from this.
The Mortal Instruments: Not as pronounced as some examples, but Clary feels insecure when she compares herself to the more traditionally beautiful, busty/curvy Isabelle.
Subverted in "The Hunger Games". Haymitch throws an absolute fit when they want to give an unconscious Katniss breast implants to make her more appealing to the Capitol audience, and wins that particular battle. When she wakes up and finds out about it she's very relieved to have gotten to keep her, at that point almost non-existent, natural bosom.
Dialog from the Veronica Mars episode "Meet John Smith", where Veronica is trying to change her flat tire:
Troy: Flat? Veronica: As God made me.
Yamada Naoko in the live-action Japanese dorama Trick is constantly teased about her flat chest by all the male characters and is quite bitter about it.
A running gag in Married... with Children is Marcy being mistaken for an adolescent boy due to her flat chest and short hair.
This, along with her short stature, is one of Claudia's main insecurities in Party of Five.
iCarly: Carly's "flat-chestedness" during early (in Season 1) and middle (season 2 or 3) puberty has been humorously referenced in a few episodes.
In "iSaw Him First":
Carly: What's that supposed to mean? Sam: Why won't you ask your new helping bra? Carly:(looks down and gasps) There's nothing wrong with a little help.
And in "iFight Shelby Marx":
Carly: I'm not a twig. I'm getting curvier every day. Freddie: I know. Carly: Eyes up, dude.
Apparently, Lizzie McGuire, Kate ditched Lizzie and Miranda as friends once she "developed", only adding to Lizzie's insecurity regarding her size. Many episodes made reference to bras, Lizzie's lack of curves, etc., which seemed unlikely towards the end of the show, when Hilary Duff got older and obviously well-endowed.
In the Taiwanese SeriesDrunken To Love You, Xiao Ru gets in a size argument with her boss. Later, she wears a bustier to a club, inciting her husband to cover her with his jacket... backwards.
Eun Bi from Flower Boy Ramyun Shop gets upset when Chi Soo justifies touching her chest as it's not much different from his.
In "A Reunion ...", the second-season premiere of Don't Trust the B---- in Apartment 23, June laments that all the stress she's endured since coming to New York has probably cost her a cup size.
Don as a joke in the Sam & Cat episode "Twinfection".
Cat: When I say Aybra Kadaybra...
Sam: I thought you wanted me to stop making fun of your A-bra.
Cat:covers her breast
In the True Life episode, "I Hate My Small Breasts", they had a woman who was an A-cup but worked as a go-go dancer and pole dancer. Of course, this led to her wanting to get breast implants.
Parodied in the stage play Psycho Beach Party, where the female lead laments her figure to the audience while topless ("It's like I have the body of a boy!")... and while played by a boy.
Val in A Chorus Line gets a song all about this ("Dance: Ten, Looks: Three"). She never grew the womanly attributes necessary for Broadway success, so she went to a plastic surgeon and got them installed. One dancer says she wishes she had one breast just like her. Val's advice, "Have 'em all done!"
Flat and sassy, I would get the strays and losers. Beggars really can't be choosers. That ain't it, kid. That ain't it, kid. Fixed the chassis; "How do you do!" Life turned into an endless medley Of "Gee it had to be you!"
Either you're a washboard or an Eiken character, and of the main female characters, only Prier from La Pucelle: Tactics, Rozalin from Disgaea 2, and Artina from Disgaea 4 are on the other end. The only average girl is Asagi.
In Disgaea Dimension 2, Laharl is hit with a temporary Gender Bender. S/he is not particularly flat chested. Laharl complains about the size of his/her chest, and Etna threatens to stab him if s/he makes that complaint again.
It's worth noting that between La Pucelle and Disgaea, there was a noticeable change in character design, mostly due to lead artist Takehito Harada taking the place of former lead Ryoji Majima.
The manga adaptation of Disgaea 2 adds the Dimension Guide Friday to this list. She's a member of the absolutely flat Archer class. Just how absolute this is is shown in a series of yonkoma at the end of the book.
In the first Disgaea, Etna and Flonne's Pettanko status is actually vital to their employment; for undisclosed reasons (possibly Rule of Funny, possibly a result of his mother's death), their master Laharl (who is himself an older-than-he-looks boy) has a deep aversion to breasts. Simply seeing a buxom woman freaks him out, and even induces weakness and nausea (one part of the game actually has a battle where a chorus of big-breasted she-demons constantly chant positive words, his other weakness, and Laharl rapidly gets weaker)- nobody really wants to know what'll happen if he actually gets sent to Marshmallow Hell or a similar situation. Being as flat as they are is the only reason he can put up with them. In fact, in the anime adaption, when Laharl faints and falls face-first against Flonne's chest as a result of seeing Jennifer, he suddenly revives and makes a confused comment that Flonne's cured him.
Their parent company, Nippon Ichi is personified in Neptunia. She is, of course, flat as a board and angry about anyone who mentions it. It doesn't help that she has her chest (wrapped with bandages where her breasts would be) completely exposed. She's pretty much asking for it.
Likewise, Norma of Tales of Legendia. She's not flat chested per se, she just perceives herself as such. It doesn't help that the other female members of the party are stacked.
For that matter, Arche in Tales of Phantasia and Anise in Tales of the Abyss (though Anise may be excused for only being 13). To be fair, though, Arche only calls herself flat-chested in the game when compared to Mint. It doesn't seem like a fair comparison when Arche tells Mint that she "has the biggest tits [she's] ever seen!"
This is the basis of a few skits in ''Tales of the World: Narikiri Dungeon 3". In one skit, Frio (the game's male protagonist) sees Arche and Calo (his female counterpart) together and begins gleefully shouting about the "Pettanko Girls". Arche joins him in teasing Calo, who responds by reminding Arche that "He said Pettanko Girls! With an 's'!" Cue savage beatings of Frio.
Ibis Douglas. In a series where girls of her age just manage to have well-endowed breasts, she happens to be a Pettanko and has no bouncing cut-ins, contrast with the other heroines. Even a loli that she took care of (in Alpha 2) has an adult form which has bigger breasts than her. Obviously her status as a pettanko has been the subject of jokes. But it doesn't stop her to be a champ of Moe girls amongst fans.
In Super Robot Wars Reversal, one of Duminuss' Loli Quirky Miniboss Squad, Tis, has this as her plight (never mind that she's a loli). In a heart-wrenching moment of sacrifice, Duminuss asked what they wanted if they are to be reborn, Tis answers, "I want a body with sexier form and bigger breasts".
And in the spinoff game Endless Frontier, we have Suzuka as the resident Pettanko. So much Aschen calls her Princess Flat/Pettanko-hime, and most of the time she's praised about being beautiful, it mostly has something to do with her exposed belly. It doesn't help Suzuka that she's in the quadruple digits in age and still has a non-existant chest.
Then there's Xiaomu, like-wise a loli. It also doesn't help the self-esteem that they're in a group with two of the bustiest women in SRW and the third one is definitely not lacking.
Chihaya Kisaragi from The Idolmaster. Her bustline, 72 centimeters, has become something of a magic number for iDOLM@STER fans. In fact, if you Google for "72cm" and set the language to Japanese, guess what the top result is. (The Japanese Uncyclopedia also lists the "Chihaya" as a unit of measure for length...) She wasn't that much of having such thing as this is mostly fandom-based. But this becomes an Ascended Meme in the anime, during the Beach Episode whereas just by looking at Azusa and Takane's assets, she lets out a dejected grunt.
Shino from Izuna Legend Of The Unemployed Ninja fits this to the point that one of the comics on the game's website refers to her as the first flat-chested character on the DS. It gets to the point that in the sequel, this is the primary description her sister gives people when trying to find her. Although it later turned out it wasn't her sister.
Lilith Aensland, "sister" of the huge-breasted succubus Morrigan in the Darkstalkers / Vampire video games is a strange inversion. Although she tends to act "as if" she didn't notice the size difference, it's the rather busty Morrigan that makes a big deal of it every time Lilith gets the attention Morrigan is craving, while Lilith is not bothered by her flatness. See Morrigan's ending in Super Gem Fighter Mini-Mix for an especially clear-cut example.
Castlevania Judgment has Maria obsessing over her relative bust size in story mode, going so far as to attack someone for not appreciating their own endowments.
Touhou's Sakuya Izayoi (pictured above) has this in many Fanon depictions, and many fans joke that she pads her bra (although it's well on its way to being a Discredited Meme). Said fanon also holds that even mentioning the word "pad" in Sakuya's presence is a Berserk Button that's liable to get you stabbed. It's worth noting that official Touhou artwork doesn't give any of the characters much of a chest, and such topics are never brought up in canon, so any A-Cup Angst a character may have in fanon is entirely due to fan interpretation or Memetic Mutation.
Eruruw of Utawarerumono although this is generally the mostly expressed sentiment. She actually tends to feel physically inferior to the entire cast (jealous of Urtoriy's breasts and hair, Touka's face, Karura's hips/effortless physical upkeep and that Kamyu has such large breasts despite being the same age or maybe younger) though they also tend to feel the same way about themselves. But even Mukkur is disappointed by her breasts. Yes, the cat. Mukkur was disappointed because she didn't produce milk, though.
Noel Vermillion. During story mode Taokaka refers to her as "lacking lady" and after their fight Noel talks to herself about ways to make her breasts grow, including having a boy massage them. Bang Shishigami mistakes her for a boy at first and she attacks him for it (in Chronophantasma arcade, Amane makes this mistake too). She also contemplates asking Litchi Faye Ling ("BoobieLady") about how to get them bigger. Litchi chases Noel around during one story path trying to get her to cosplay as various things, including May, the loli pirate from Guilty Gear, because the costumes don't fit Litchi.
Even though Tsubaki has way bigger breasts than Noel, she does get into a bit of this when Taokaka gropes her breasts and calls them "average".
Kokonoe has some issues with her chest size as well (Noel is the only one smaller than her). Near the end of Noel's Help Me!! segment, Noel points this out and Kokonoe chases her off the stage. In Makoto's, the two of them have a chat and, when breast size gets involved, Kokonoe almost throws a tantrum (Makoto's the inverse - she's smaller than only Litchi, and a display◊ shows up to compare them). If Relius' CS gag reel is to be trusted, Makoto is very aware of Kokonoe's breast envy.
Makoto as Ragna: Kokonoe, did you steal my boobs?
Platinum the Trinity, though, despite having the size of Rachel, takes this Up to Eleven in her Gag Reel and features Luna having a dream where she had to unite with many of the small-chested ladies (minus Kokonoe) and the Clovers to fight against the 'Boing Queen' (Litchi depicted as an Evil Overlord, hammy at that) in a parody of a Magical Girl battle. 'Boing Queens minions include the top three bustiest ladies in the setting (as seen in the picture above), Arakune, and Ragna. Since this IS Luna's dream, one can wonder just how insecure she is to her own breasts, despite her age. Oddly, Trinity Glassfille (mistranslated in Extend'' as Glasssfield), one of the souls residing in Platinum's body, seemed to have no problem with her original body's breasts (big it was).
Leanne/Reanbell from Resonance of Fate has much attention drawn to her breasts' lack of size, mostly by Vashyron. She tends to react with violence whenever it happens, although her insecurity is somewhat justified by the fact that she's 21 but looks like she just hit puberty.
If we are to believe Ayla, Marle from Chrono Trigger is one. Ironically, Lucca is visibly flatter than Marle, but doesn't get any flack about it.
Puella Magi Madoka Magica Portable: In Homura's True Ending, when Sayaka forces Kyoko into the old school uniform of the large-breasted Mami, Kyoko takes great offense at Sayaka's comments about the chest area being loose. Madoka and Homura's dialogue after this exchange implies that Homura is going through this, too.
Akiha Tohno, the TsundereOjou, is well aware of her small assets, but that doesn't really prompt out until the more intimate scenes in her route of the game ("'I have small breasts, so I was scared you might not like them.' Akiha is blushing so hard that even her ears are turning red..."). Fanontook this aspect of her personality and ran with it.
The sorta-sequel Kagetsu Tohya features one possible path where Shiki walks in on her changing and, for some reason, is compelled to comment that her chest is "steep as a cliffside". Unsurprisingly given the nature of the characters involved, this leads to a Bad End.
Added irony: Akiha and Saber have the same bust size. Saber, however, is more likely to have her breasts overstated. Rank B Charisma can go a long way.
Becomes an Ascended Meme in Carnival Phantasm when Shiki comments on how Akiha has grown in every parts except her breasts, even being regressed into a 4-years old mentally didn't stop her to turn red and presumably beat the shit out of Shiki.
Saber of Fate/stay night, once she starts to develop feelings for Shirou, shows discomfort over the fact that she doesn't have a better figure. During her date with Shirou at the pool in Fate/hollow ataraxia, Lancer makes the mistake of saying that a bikini is for more mature women- At which point Saber proceeds to kick his sorry ass all over the pool.
Rika Furude of Higurashi no Naku Koro ni berates herself for this, despite being twelve years old. Rika's technically centuries old. The constant time loop that she goes through keeps reverting her physical body back to a younger time point, and she never reaches puberty. Near the end of the series, she resolves to grow up to have huge breasts, which is a lot more poignant than funny, given the context.
In the anime adaptation, there's a short bit at the end of episode 5 of season 2 where Rika grabs Mion's boobs and declares "I won't lose!"
In one of the OVA episode, she has a dream where she's a grown up Magical Girl. The first thing she does when she wakes up is feel her chest and make a sad expression.
Setsuna Kiyoura from School Days. It doesn't help that both her best friend (and half sister, in the games) Sekai Saionji and her love rival Kotonoha Katsura are much better endowed.
Kazuna in Kara no Shoujo. Reiji jokes that while her belly may be big due to pregnancy, her chest is as flat as ever.
Nayuta Kagura, to the point where she lies about her body measurements and to a lesser degree, Kirara Kurokawa, in which mentioning how small she is tends to elicit threats of violence from her, from Yumina The Ethereal.
If My Heart Had Wings: Occasionally, Kotori shows nervousness that Aoi won't be as attracted to her because of her modest chest, even though she's normally pretty confident about her looks. Though considering she has Amane and Ageha to compare herself to, it's probably no wonder.
Quinn from Shotgun Shuffle has held a secret grudge with her roommate Ellie for years over this.
In Peter Is the Wolf, we meet Cherry, a Chinese-American Were-Raccoon-Dog (don't you dare call her a Tanuki!) of modest proportions in human form who is inordinatly proud of the D-cups she sports in were-form... until she sees the were-forms of Sarah the Werewolf and Ashley the Were-Vixen. Sarah herself, in her human form, isn't exactly big either, thought it seems to vary from page to page.
Flora from TwoKinds, mostly as compared to other Keidrans(Kat and Natani in particular). Her human lover Trace certainly doesn't seem to mind...
MegaTokyo. Although she doesn't seem too self-conscious about it, it's been noted that Nanasawa Kimiko is rather flat-chested — both in her initial appearance at Anna Miller's, when she apparently was wearing inserts to work, and again during Piro's conversation with Tsubasa over the internet after Kimiko's radio outburst makes her an instant star.
In her sometimes semi-autobiographical webcomic The Fart Party the author/artist Julia Werz tells of the day in the 7th grade when a cute guy that she had a crush on sat next to her in the lunch room and out of the blue asked her what her bra size was. She was so surprised that she immediately blurted out "32AA" without thinking and was known as "Tiny Tits" for the rest of the school year. 
Kiley from Ménage ŕ 3, so much so that when she dreams of being a professional therapist, she also dreams of having large breasts to go along with it, and when Yuki mentioned that her girlfriend had small breasts too, she cried tears of joy.
Played with a little in Alice when the girls get their first training bras and none of them are developed enough to show — so Joanne stuffs her bra with tissues to make it appear that she's got huge breasts. Nobody's fooled for even a second.
Karin-dou 4koma: Seren and Tamaryu are very sensitive about their flatness. Seren's reactions in particular range from fury, to padding her chest, to locking herself in her room. But somehow, her genuine angst is actually deliberate, to make her immortality more interesting. Her unsealed form is actually reasonably endowed.
A minor source of angst for Wonderella in The Non-Adventures of Wonderella, to the point that in this comic she goes to Dr. Shark for breast augmentation. He asks her to not do it just out of societal pressure and consider what body feels right for her.
Although we don't see her angsting over it much, Ellen "Elf" Foxworthy of Schlock Mercenary does get teased early on that when not in her much curvier powered armor, she "doesn't get mistaken for a woman" very much, and apparently joined up with the mercenaries under the pretense of being a boy. Later on when she gets a full body rebuild, her two main requests are longer legs and bigger boobs.
In thisCaptain SNES: The Game Masta strip, Lucca is implied to suffer from this trope via an unexpected revelation from Gato, who thought he was praising her and the signs of her "perfection" but ended up giving a Compliment Backfire speech. The main problem is she made the mistake of giving him a rough neural map of her brain as part of his AI, which apparently included her memories as well.
Also, played with in the Ayla stories, where Ayla helps one person at powers testing get implants to fix this, and get the guy she likes. When one of her own close friends wants Gag Boobs to become a stripper... Ayla rejects that whole-heartedly.
Jade Sinclair (Generator) is closer to the flat girl who worries about her lack of size and maintains that childishness too. In fact, she still looks like she's about eleven.
When in costume, Bungie of the Global Guardians uses her Rubber Man powers to increase her bust size as part of her "disguise". She's normally rather small-breasted, and figures if people are looking at her chest when she's in costume, they won't be looking at her face.
Foxy from Zorak's let's play of Pokémon Quartz after a certain trainer told her to take off her pants and jacket and then losing:
Roker(sic) Travis: All the small things... Foxy: Hey, I’m not that old, I know I’ll fill out later.
Taylor, the protagonist of Worm, wears her hair long specifically because she feels herself to be lacking other feminine features.
W.I.T.C.H. has Wilhelmina "Will" Vandom, a boyish-looking redhead who is openly displeased with her chest's small size, and Hay Lin who has similar concerns about her undersized breasts. They grow up (and how) in Guardian form, pumped up to about D-cups, and much happier for it. Will is especially prideful about her buxom Guardian body. In the first episode, while the girls are looking at their newly transformed selves, Hay Lin says "look what we have behind us" (wings), and Cornelia responds "look what we have in front of us" and looking at a slight downward angle. There was nothing in front of Cornelia.
Sharon Spitz, the title character of Braceface, is constantly and excessively insecure about her chest, being completely flat-chested. So much so in fact that she tried on one episode to increase her breast size with a pneumatic pump...
This is one of the reasons that Hayley on American Dad! is such a bitch, as she's apparently bitter about not "filling out" the way she wanted. One episode had a flashback to her early teens when she angrily screams at her parents "This is as big as they're gonna get?!" and then torches the house in anger.
A throwaway line hints that Angelica is this on Rugrats: All Grown Up!. Apparently she's a little bitter that her bra-stuffing campaign didn't turn out the guys like she wanted. Considering she practically has no breasts even when she stuffs her bra, one wonders if her chest is concave without it.
Despite not being flat-chested, Jen is this (especially around her sister, who is much more buxom).
Conversely, Caitlin is flat-chested, and is revealed to pad her bra.
Subtly done in Phineas and Ferb. Candace goes to Jeremy's pool party, but when she sees him there, he's chatting with a blonde, busty, curvy girl who's wearing the same swimsuit as her. When Stacy tries to calm her down after she freaks out, Candace responds with "She wears [the swimsuit] better!".
This angst is very common. The Other Wiki says that, according to the American Society of Plastic Surgeons, breast augmentation is the most commonly performed cosmetic surgical procedure in the United States. More than 300,000 (you read that right) were performed, only in 2007, only in the USA. Some of the pictures on the webpage are NSFW.
Pornstar Kitty Jung, pre-implants. Also pornstar Melissa Ashley, which caused some authorities to believe her films were actually child porn.
The Thai government is concerned about nationwide A-Cup Angst that compels many women to go under the knife. In response, they have endorsed an alternative to breast enlargement surgery known as the "Thailand Breast Slap" said to enlarge feminine assets by one to four inches. For those of you that would like to know, four inches of growth would enlarge small A-cups to full D-cups.