Origin of Skank : In the late 1960's there was a bus company called Schaenck Bus Lines. The floors of the busses were covered with crud, like the kind found on movie theater floors,under the seats. Rumors accused Schaenck (pronounced skank) of using company busses to haul garbage to the dump at night, a job normally reserved for garbage trucks. In 1970, I asked a bus driver what the filthy crud was under the seats and he replied "That's Schaenk!" refering to the president of the bus company. Someone overheard and, not knowing the the name on the side of the bus was was pronounced skank, added the word to her vocabulary. Within the year, skank became a synonyn for dirty filthy crud, or greasy grimy scum.
Schaenck went out of business and the busses are now operated by the Metropolitan Transportation Authority.
By the mid 1980's , skank also came to mean a person, usually a heroin addict, who doesn't bathe and wears grungy