The Smoking Jacket
This wardrobe element was extremely popular in the 17th century through the 1950's, but has suffered a significant loss of popularity nowadays. People wearing it today could be noticed on rare occasions, such as special gatherings, balls, celebrity events, etc.
It was an overgarment with high demand once, a thing no real gentleman would ever consider ignoring. The history of the smoking jacket goes as far back as the second half of the 19th century after the country squires decided to adapt the lounge jacket, usually worn outdoors, to a soft velvet jacket to wear while smoking after dinner. The material they used was the same as for their dressing gowns - soft velvet, that's why gentlemen preferred smoking their pipes or cigars after dinner when ladies were taking a nap, and could behave a little less informal. The key reason for inventing the smoking jacket was the willingness to protect the clothes of a gentleman from absorbing the smoking odor.
Here's the definition the Gentlemen's Magazine of London gave to the smoking jacket in the 1850's when people were still confused about the purpose of these clothes:
"a kind of short robe de chambre, of velvet, cashmere, plush, merino or printed flannel, lined with bright colours, ornamented with brandenbourgs, olives or large buttons".
The new style jacket was granted its official status after the Queen's Victoria's eldest son, the Prince of Wales, started wearing it on every occasion. Of course, the jacket has changed its style and fabric; it was no longer made of velvet but mostly from silk and sateen, and could be worn both on informal and official gatherings.
The smoking jacket (or simply the smoking, as used in some languages) has been very popular since then, and was always in high demand and en vogue until 1950's. People were not interested in smokings by that time, and preferred choosing from something more modern. The most famous devotees of the half of the 20th century were Fred Astaire, Frank Sinatra, Cary Grant and Dean Martin.
The only person who is still wearing it nowadays is Playboy tycoon Hugh Hefner who was never seen without wearing one. The well-known magazine Cigar Aficionado has even suggested the idea of bringing back the smoking as an "alternative type of formalwear" in his Jan/Feb 1999 issue. But no one seems to ever support this thought.