A Cake Eater was a well dressed loafer who usually hung around drug stores or outside movie theaters - they usually had no fixed employment. He was called a Cake Eater because he spent much of his time sipping sodas and eating cakes bought with his parents money. They were notorious for never picking up a check if they could help it.

 Another name for a Cake Eater was a Bun Duster or a Jellybean. Sometimes Cake Eaters were Mashers, but not always. Sort of like the earlier Dandy or Fop, and President Roosevelt called them Mollycoddles (he meant it in a more political way, in terms of soft voters who voted only in ways that protected themselves, but newspaper reporters used it more generally). Later they were called Drugstore Cowboys (a ‘dude’ who hung around the drug store). 

A lot of the time the terms were used derisively, to insult the man’s masculinity - Dudes, Mollycoddles, Cake Eaters were all considered “soft” and “sissies”, but a lot of Cake Eaters (and Jellybeans and Drugstore Cowboys and the rest) assumed their mantles happily and defended the names proudly!