Rudy's is still there, but it's on 9th tween 43/44 with the big pig still there. I lived at 405 West 45th (The Chatsworth) for a few years - a door down from Zanzabar (no longer there) on the NW corner of 45th and 9th and a block north of Rudy's. The song is about booze, drugs, hooking, et al...she starts out "high" in Rudy's and goes downhill from there, just like the relationship.Rudy's in NYC is (was) a bar/hangout on the lower west side. In later years the "pro's" moved further north, but at that time it was around there they were all on the stroll from Greene St to the lower 20's. A Black Cow is an alcoholic drink.
All of these guys denied this song was about drugs until their very ends, so....