Muscle Angst

A lot of body-image issues are related to/centered around femininity. Thus, we have tropes such as Big Breasts, Big Deal, A-Cup Angst, Hollywood Homely/Pudgy/Thin, Fat Girl, and so on. But the same way that thinness and breasts are associated with femininity, muscles are associated with masculinity. Thus, this trope, in which a character angsts about having not enough or too much muscle. There are two versions:

Not Enough Muscle: The Always Male version. A weak or skinny male character angsts about not being muscular. The focus may be on how this affects his success with women, his usefulness in sports/combat, or his attractiveness. If the focus is on his success with women, Weakness Turns Her On may come into play as a solution/counterpoint. Unlike breast size, which is mostly unchangeable without surgery, it is possible to build muscle, so whether this trope is justified or not depends on there being a health reason for the male being incapable of doing so.
Too Much Muscle: The Always Female version. A female character, usually an Action Girl worries that her muscles are unattractive to men. This version is similar to No Guy Wants an Amazon. Just like Weakness Turns Her On may come into play in the first version, Hot Amazon or Amazonian Beauty may come into play in this version.

Examples of Muscle Angst include:

Advertising

The ad for Charles Atlas where a bully (inadvertently) kicks sand in the face of Mac and his gal. Allegedly this actually happened to the real Charles Atlas before he started doing dynamic tension.
Mixed with A-Cup Angst in an ad manga for Chasteberry E breast enlargement pills: the Pettanko tries out all kinds of hoo-hah gimmicks to make her breasts grow, including drinking milk, using a suction device, and doing dumbbell exercise... The last one of course does nothing to increase her mammary mass but gives her muscled arms, which she regrets.

Anime and Manga

Saber in Fate/stay night thinks she's too muscular. Not that you can tell by looking at her.
- Some promotional artwork of her leads to Informed Deformity.
The comedic manga Short Cuts has a story in which a typical "kogal" gets trapped in a sumo wrestler costume and is forced into actual sumo competition. Eventually, she manages to get the zipper unstuck, only to find out all that exercise has made her unfashionably muscular. Not to worry though, a passing man still wants her... for the military!
Biske of Hunter X Hunter explains that the reason that she stays in her Sleep Mode Size is that her regular form is "too bulky".
Casca from Berserk complains that the fancy, frilly gown she dressed up in for a ball looks weird because she's too muscular. Now Casca is toned, but the fact that every male character thought she looked irresistible proves her wrong.
Variation in Pokémon Special. Ruby claims that he doesn't train his Pokemon for battles in fear that they will gain ugly muscles. Looks like to be a case of Muscles Are Meaningless, as it turns out his Pokemon are in fact very powerful and well-trained.

Film

In The Rocky Horror Picture Show, Dr. Frank-N-Furter created Rocky because he wanted a man with muscles. Frank insults Brad's lean build, and Brad's fiancée Janet replies that she doesn't like a man with too many muscles. Later Janet sings she is a muscle fan after having sex with Rocky.
Steve Rogers, whose health problems and weak build keep him from joining the army and getting girls, before he becomes Captain America.

Live Action TV

The 2005 TLC documentary The Man Whose Arms Exploded looks at an extreme degree of male Muscle Angst leading to steroid abuse and (in the case of bodybuilder Gregg Valentino) injecting oil into the biceps. Can be seen starting here (warning: some Nausea Fuel and a fair bit of bad language).

Video Games

Super Robot Wars Original Generation: Lune Zoldark complains that, regardless of her diet or exercise routine, everything she eats turns to muscle.
The Sports Club Manager Arcana from Persona 3 has a case of this. She's tanned and toned, but other girls tell her that No Guy Wants an Amazon. A likely case of Truth in Television as the game takes place in Japan, and girls (currently) avoid tans and aim for that "fragile" kind of thin.

Web Original

A Vocaloid fan video by Kagome-P had Gakupo depressed over his lack of muscle mass, and his story of emulating figures such as Alex Armstrong, Mantaro Muscle and an assortment of anonymous, heavily muscled figures in order to woo the girl of his dreams. This backfires at the end of the video, when he discovers that she's now into skinny guys and his struggle to get a toned body was for nothing.

Western Animation

Milhouse on one of The Simpsons episodes that takes place in the future.
The first ever Cutaway Gag in Family Guy showed a skinny and weak Adolf Hitler in a gym glaring angrily at a musclebound Jewish man surrounded by beautiful women.
A Running Gag on Ren and Stimpy is Ren wishing for huge pectoral muscles. The episode, Ren's Pecs finally grants him that wish, allowing him to beat up a beach bully, attract several girls, and become a movie star and male model.