Location: Montmartre, Paris (Bohemian sector)
----- is the practice of an unconventional lifestyle, often in the company of like-minded people, with few permanent ties, involving musical, artistic, or literary pursuits. In this context, Bohemians may be wanderers, adventurers, or vagabonds.
This use of the word bohemian first appeared in the English language in the nineteenth century to describe the non-traditional lifestyles of marginalized and impoverished artists, writers, journalists, musicians, and actors in major European cities. Bohemians were associated with unorthodox or anti-establishment political or social viewpoints, which often were expressed through free love, frugality, and—in some cases—voluntary poverty. A more economically privileged, even aristocratic or wealthy, bohemian circle is sometimes referred to as haute bohème ("high bohemians").
The term Bohemianism emerged in France in the early nineteenth century when artists and creators began to concentrate in the lower-rent, lower class, Romani neighborhoods. Bohémien was a common term for the Romani people of France, who were mistakenly thought to have reached France in the 15th century via Bohemia.
This was a difficult one, as it's difficult to find examples of fashion from a subculture that, by definition has informal and unconventional social habits. Generally, this also meant that they pretty much disregarded the fashions of the time (especially more evident in women's clothing). These people lived for their passions to the point where they'd pursue them... regardless if it brought income or not (and it most often didn't).
That being said, from what I could see, the sack suit was still quite popular for men's casual clothing.
The setting was inspired by Le Chat Noir which was right smack in the middle of the bohemian Montmartre District, and "is thought to be the first modern cabaret: a nightclub where the patrons sat at tables and drank alcoholic beverages while being entertained by a variety show on stage.". So here, we have Monsieur Leighton enjoying the cabaret atmosphere with a drink, while continuing to write his current story.