La bronca is a colloquial word that can mean "a telling-off" or "blame" in an argument. It's vivid and informal, perfect for capturing real, everyday Spanish.
In the song, Xavi sings "Y no me eches la bronca que fue culpa de los dos" (And don't give me the blame/telling-off because it was both our fault). He's pushing back against being made the sole villain, making this a key word for understanding the song's central conflict.
Ever been blamed for a breakup that wasn't totally your fault? That's the whole mood of Xavi's "El Malo". He kicks things off by admitting the relationship is over. Even with love, he says, "no nos entendimos" [we didn't understand each other]. He's accepted it, but he has one big problem: she's telling everyone that he's the bad guy.
He calls her out on this with a simple question: "Si soy el malo de la historia / ¿Por qué en la peda se te olvida que me odias?" [If I'm the bad guy in the story, why do you forget you hate me when you're drunk?]. It seems that when she's had a few drinks, she starts acting like his girlfriend again and even sends him pictures of her beer. But the next day, when she's sober, she pretends nothing happened. He's tired of being the villain in her story when her late-night messages tell a completely different one.