A bum, homeless person, or undesirable of either sex. The term does apply to street musicians, the working poor, or temporarily homeless people who keep themselves tidy. It also does not have racial connotations. Rather, it refers to people who are poor, filthy and homeless as a result of their own character flaws, such as laziness, surliness, alcoholism, drug addiction, etc.
"Boy, there are a lot of rub a dubs downtown today. Is somebody giving away hot dogs?"