In United States slang in the 1910s and early 1920s a Jelly bean or Jellybean was a young man who made great effort to dress very stylishly (usually to attract women) but had little else to recommend him; similar to the older terms dandy and fop and the slightly later drugstore cowboy. However, the word was also used as a synonym for pimp. (Today a "jelly bean" might be known as a metrosexual.)
The jelly bean type was memorialized in the song, "Jelly Bean (He's a Curbstone Cutie)", kept popular through the 1940s by Phil Harris. It was written by Jimmie Dupre, Sam Rosen, and Joe Verges, and published in New Orleans in 1920 by Universal Music Publishers, Inc.
NOTE: This is based on hearsay, not direct observation. -- ed.