I used to rap about nothin', now I rap about nothin'
But that nothin' was somethin' that ain't nobody was bumpin'
He’s saying he used to “rap about nothin'”, as in his early stuff from Sick boi and up through earlier tracks on Camp it was often about how little money he had, how he grew up in poverty.
He moves from that regard to now where he “raps about nothin'” as in lyrics that sound good but don’t have any liberationary meaning, they’re just “money, hoes and clothes”.
The second line is commenting on how people listen to the “money, hoes and clothes” stuff more than his earlier, more meaning-laden work.
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