She runs shit, she's the jock, I'm the horseshoe
A jock (or a jockey) rides a horse, and horses wear horseshoes. The girl he’s avoiding isn’t riding him, she’s stepping on him (metaphorically). The line could be heard as “whore’s shoe”
This also means that Earl is even lower than the horse. The jockey controls the horse, and the horseshoes are nothing but an afterthought and are easily replaceable — Just like this girl seems to think Earl is.
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