Lyric discussion by CuteSparkina 

The Black Cow can be a candy-like mixed "high-powered" beverage or it can be indeed a rootbeer float. Our Hero is telling The Lady that he is INDEED through being this lady's sounding board every time one of her relationships with unsuitable fellows goes sour and she comes running back to him. In the cocktail context, a "black cow" is considered a frou-frou party-girl drink. Or, in the context of an ice-cream parlor kiddie beverage, Our Hero is telling the lady that she is acting like a twelve-year-old

I think you nailed the essence of the song here.

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