From Billy Joel's Keeping the Faith:
I put on my shark skin jacket
You know the kind with the velvet collar
And ditty-bop shades
What are ditty-bop shades? I can buy a pair, or could if they were still in stock, but that doesn't help me in distinguishing them from any other sort of sunglasses.
So, to put the question another way, what makes those particular sunglasses, and not other seemingly similar ones, "ditty-bop shades"? What does "ditty-bop" mean?
Research: my Pocket Oxford was no help, and neither was Wiktionary or Wikipedia. The only directly relevant thing I found on Google was the Amazon link. "Diddy bop" means "cool" according to the Online Slang Dictionary, which might be related etymologically, but it still doesn't tell me what in particular about "ditty-bop shades" made them cool. (Google also found some images, but they just left me even more confused as they seemed to have little in common.)
Best Answer
The slang term dittybop has a rather complex history. According to J.E. Lighter, Random House Historical Dictionary of American Slang (1993), dittybop is a variant of diddybop, which was in turn originally a variant of diddlybop. The first form of diddlybop that Lighter cites is as a verb:
Related to these senses of the word is the noun diddybopper—"one who diddybops; (hence) a young street hoodlum"—which Lighter finds in print as early as 1958. Meanwhile, a second meaning of diddybop/dittybop as a noun was emerging:
Yet another meaning of diddybop/dittybop as a verb emerged in the late 1980s:
Though this sense of the term arose comparatively recently, it seems remarkably close to the originally bebop sense of "diddly bop! diddly bop!" that Lighter notes in the first block quote above.
And finally Lighter has this entry for diddybop as an adjective:
It's interesting to compare this disparaging sense of diddybop with David Bowie's use of bipperty-bopperty in his 1971 song "Queen Bitch":
Clarence Major, Juba to Jive: A Dictionary of African-American Slang (1994) has this brief but precise entry for dittybop:
Robert Chapman & Barbara Kipfer, Dictionary of American Slang, third edition (1995) has this for dittybop and dittybopper:
Chapman & Kipfer's take on diddlybop difffers significantly from Lighter's:
Given that the online slang dictionary cited in the poster's question defines diddy bop as "cool," we have multiple ways to interpret the meaning of dittybop in Billy Joel's "Keeping the Faith" (which was released in 1983). Since the speaker in Joel's song uses "dittybop" to describe his own fashion choice in eyewear, we can safely discard the disparaging meanings "offensive," "foolish," "ugly," and "pseudo-hip." More likely, the intended meaning is something like "characteristic of a hipster who walks with a swagger or a rhythmic sway." If so, "dittybop shades" are simply sunglasses that a hipster or street-cool guy of the relevant era would wear. (Because the song is retrospective, the era in question is probably the middle to late 1960s, not 1983. Joel was born in 1949.)