Negative in my life, scream that till I'm hoarse
He is saying “negative” in my life. This is tied to the previous line about the people he is cutting off. Despite all the success he has attained, (i.e. owning a porsche), he still feels negative constantly and will continue to tell that in his music, (i.e. scream that until he’s hoarse).
Horse could also refer to the game of H.O.R.S.E. where you lose if you accumulate all five letters after missing five shots that your opponent made.He will be rockin' with TI until he dies/loses/his career ends.
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