The story
Like yuppie flu, the term originally connoted (and may still connote) contempt by working-class people for others who are perceived as rich, undeserving, and soft. The stereotype-laden imagery is that a yuppie throws twenties around like a poor person might throw food stamps around, neither one wholly deserving the resource that they are profligately consuming. Class antagonism is implicit in both directions, upward and downward.
Etymology from Wiktionary, CC BY-SA 4.0.