In The Collected Piano Works" of Scott Joplin, the second intro (by Rudi Blesh) states:
“As for serious acceptance, ragtime fared better in Europe than at home where its **very name **was an epithet, a scornful belittling term with strong racial overtones.” (My bolding.)
Specifically, what in hell is/was the epithet?
“Another thought is that this type of music was used in saloon bars where prostitutes were not available, as they were ‘on the rag’.”
But that strikes me as terribly weak, maybe even too convoluted, especially that Ragtime seemed to have become popular, first in whorehouses where there were always some babes ready and able.
Most other sites, such as reference.com tie the term to the musical time such as
The etymology of the word ragtime is not known with certainty. One theory is that the “ragged time” associated with the walking bass set against the melodic line gives the genre its name.
No epithet in that context, I think.