Uniform Refusal

A character who refuses to wear a uniform, despite being in a situation where on is expected of him. This may be a form or rebelling against authority, due to practical concerns about an impractical uniform, or because they don't think they deserve it.

Compare Custom Uniform, where they wear the uniform, they just change it first.

Examples of Uniform Refusal include:

Anime and Manga

Edward Elric of Fullmetal Alchemist wears a distinctive red coat instead of a uniform, despite being employed by and Mangaa rank in the state military. (The Amestrian military also seems more than fairly lenient when it comes to how its officers wear their hair.)
Ranma Saotome of Ranma ½ never wears a school uniform in either the manga or the anime, unless it's a girl's uniform as part of a plot to manipulate Kuno, or a disguise to fool Ryouga.
In Hana Yori Dango, the F4 -- the four richest and most popular kids in the school -- never wear their uniforms.
In Sket Dance, Shinzou, the Kendo club captain, is constantly cosplaying as a samurai, so that even when he's in school he wears the traditional samurai outfit instead of the school uniform. In one episode, he's seen getting chastised by the martinet Student Council vice-president for it.
Manjoume in Yu-Gi-Oh! GX when he returns to Duel Academia.
Because he harbors the spirit of the cat, Kyo from Fruits Basket doesn’t wear a tie as put of his school uniform since most cats hates collars.
- Rather than a male’s uniform, Momiji wears a girl’s uniform with shorts instead of a skirt. Kyo calls Momiji out on this and so does the president of the Absurdly Powerful Student Council, Makoto Takei, who wouldn't allow a boy to wear a girl's uniform, even if the school doesn't mind … until Hatsuharu intervenes. Hatsuharu doesn't wear a tie either, and he makes a stand about it.
- In a later episode, Ayame had ran into problem with his long hair, even though the school didn't mind it being white since they correctly assume it was natural. Ayame was able to convince the school else wise. We later learn he too was on the council during his high school years and changed some of the rules.

Literature

In the Johnny Maxwell Trilogy, the Good Old British Comp attended by the main characters has a uniform but doesn't enforce it, to the point where only Yo-less wears it. Which, according to Wobbler's logic, means that jeans and T-shirts are the real school uniform, which means Yo-less is out of uniform.
Corran Horn in the X Wing Series keeps his flight suit and X-wing colors from his days in Corellian Security -- mostly because his X-wing was his personal property, rather than assigned to him by the New Republic.

Live-Action TV

Gentaro in Kamen Rider Fourze still wears his blazer and jeans, complete with fire-patterned Chuck Taylors whilst everyone else wears the school uniforms (sometimes with their own adjustments, but they're still the same basic clothing). It doesn't look like he's going to change them any time soon.
- Even more so because, according to the school rulebook that's shown in #17, the school uniforms are recommended but not required. Ohsugi got really angry when he read that.
House very rarely wears the white lab coat required for doctors at his hospital. Vogler, the hospital's chairman at the time, tries to get House to wear one in the first season. Apparently this is in line with Fox's desire for a medical show without "white coats going down the hallway."
Before the accident, crew members on Red Dwarf wore khaki fatigues or boiler suits. Lister wears a jacket with an assortment of badges sewn onto it and a London Jets t-shirt along with his Nice Hat. This is mostly because Lister isn't comfortable with anything too military.

Web Comics

El Goonish Shive has a whole arc about Moperville North High School introducing uniforms when Principal Verrückt was hit by one of his insane ideas. Naturally, Susan objected immediately and at the top of her lungs on the grounds of no way she's going to wear skirt, the rest of the school quietly seethed... all the fun. Her follower even got on local TV before the arc terminated rather anticlimactically due to sudden backdraft of sanity allowed into it.