And penny loafers though I had the nickel in mines
There are two levels of wordplay in this line.
The first is a play on words based on a type of shoe known as penny loafers.
Common had an inflated sense of self worth and therefore his penny loafers felt like he had a nickel in his. Others' penny loafers were literally less valuable than his.
The second meaning is in the phrase “nickel in mines.” This refers to both his penny/nickel loafers and nickel, the silver-colored metal that is mined.
This builds on his inflated sense of self-worth: Common thought he had the nickel in mines, or wealth and importance. He also felt as though he had uncovered something special and valuable, perhaps like the pieces of lyrical wisdom that he had mined from his mind.
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