"Beatnik" was a more superficial and aesthetic spinoff of the beat movement. The word was coined by Herb Caen, a San Francisco columnist, in 1958, playing off of the recent launch of the Russian sputnik.
Madison Avenue embraced the term, and used it to sell a certain bohemian "look." The look advertised was something between a 1920s jazz musician and a bohemian New York artist.
Black turtlenecks, goatees, black and white striped shirts, phony "impressionist" poetry readings, bongos, berets and other aesthetic trappings were all part and parcel of "the beat experience."
These stereotypes were also perpetuated through cartoons, B- to Z-grade movies, songs, and other popular imagery of the day. The character Maynard G. Krebs, in the American sitcom "The Many Loves of Dobie Gillis," solidified many of these cliches.
Were there ever any beatniks? Probably, but they were as phony, or phonier, than the hipsters of today. Instead of being a vital social or artistic movement, this was a way for ordinary people to feel "bohemian" without actually taking any risks, or producing anything of value.
Jack Kerouac, who coined the phrase "beat generation," hated the term. (Wouldn't you?) Allen Ginsberg famously said that "If beatniks and not illuminated Beat poets overrun this country, they will have been created not by Kerouac but by industries of mass communication which continue to brainwash man."
This appropriation of beat culture mirrored the later co-opting of the term "hippie," which grew into a grotesque parody of itself by the late 1960s. In point of fact, the word "hippie" grew out of the word "hipster," which was used to describe various bohemian types who lived in NYC's Greenwich Vilage, and Haight Ashbury in San Francisco. Like modern-day hipsters, 1950s and 60s counterparts shunned work in favor of artistic expression; or, at least, pretending to be artists.
The word is still in use today, though its negative connotations have largely faded. A Haruki Murakami book, Sputnik Sweetheart, gets its name from a catachresis by the narrator's love object, who says "sputnik" instead of "beatnik." Film director John Waters once cited Maynard G. Krebs as an inspiration growing up. Unfortunately, it's the cliched image, of sunglasses, turtlenecks and bongos, which lives on...not the reality of the beat generation.