Farrapo literally translates to "rag" or "tramp". It's a strong and somewhat archaic word that isn't commonly heard in everyday conversation or many songs.
In this song, the singer uses it to express how he feels mistreated and devalued by his former lover. He asks, "Para me tratar assim como um farrapo?" (To treat me like a rag?), highlighting the depth of his pain and the disrespect he feels. This vivid imagery makes the word particularly impactful.
Gusttavo Lima spends this entire song asking one question and never getting an answer. "Que mal te fiz eu?" (what wrong did I do to you?) opens every chorus, and each time he adds another piece of evidence: "Para me tratar assim como um farrapo" (to treat me like this, like a rag), "Um vagabundo, um pobre coitado" (a bum, a poor wretch). The verses that set it up are smaller and more everyday, which is what makes them sting. She turns her head when they pass in the street, "E viras a cara" (and you turn your face away), and she is telling people things about him he cannot recognise, "Todo esse veneno" (all this poison).
What lifts it above ordinary heartbreak is how far he pushes the accounting. The breakup already happened; his question is why it has to keep going. "Já não bastava ter matado o nosso amor" (wasn't killing our love enough already), then "Não te bastava a dor que teu adeus deixou?" (wasn't the pain your goodbye left enough?). By the final chorus he has reached crucifixion, "E quer me ver crucificado ainda" (and still want to see me crucified), which is a lot, and the sertanejo arrangement behind him is entirely comfortable with that. The outro just repeats the plea, "Diga que mal te fiz eu" (tell me what wrong I did to you), and the song ends with the question still open.