Necio translates to "stubborn" or "foolish." It's a strong word that goes beyond simply saying someone is 'difficult' or 'silly.'
In the song, KAROL G uses it to describe her ex-lover's persistent and unyielding nature, especially in his refusal to acknowledge her pain. She sings, "Tú eres necio, pero te disfrazas, haciéndote el ciego cada vez que yo lloraba" (You are stubborn, but you disguise yourself, playing blind every time I cried), highlighting his deliberate ignorance and emotional unavailability.
KAROL G is looking back at a relationship that's fallen apart, and she's not holding back. She starts by asking where everything went wrong: "¿Qué fue del amor? ¿Del éxtasis?" (What happened to the love? To the ecstasy?). She feels like she lost out by putting him first, singing that happiness always "se me escapa de los dedos" (slips through my fingers) when she's with him. It's a classic story of remembering the good times, like celebrating on a plane to Paris and planning a future, but realizing the person she loved has changed, or maybe was never who she thought he was.
But this isn't just a sad breakup song. There's a powerful shift. She declares, "Te llevas to' menos mi dignidad" (You take everything except my dignity). She's keeping her self-respect. She also uses a very Colombian phrase, "No pienso darte agosto nunca más," which means she's not going to let him get away with anything ever again. And then... well, the song ends with a list of some very strong Spanish insults. It's a blunt, angry, and totally honest way to say she's done for good.