Gancho al ego literally translates to "hook to the ego." It's an interesting and somewhat colloquial phrase that isn't commonly found in every song.
In the context of the song, it refers to a jab or a blow to someone's pride or self-esteem. The singer uses it to describe how he's delivering another emotional hit to his ex, asserting his superiority and making it clear that she won't surpass him. It's a vivid and memorable way to express emotional one-upmanship.
Eden Muñoz brings us a breakup anthem with "Juro," where he's making a big promise to himself: he's going to get over his ex, and fast! He declares, "Juro que voy a echarle muchas ganas No va a pasar de esta semana Para que olvide por completo lo que fue" [I swear I'm going to try really hard It won't be past this week For me to completely forget what was]. He's so sure he doesn't want them in his future, saying, "Jamás estuve tan seguro De no quererte en mi futuro" [I was never so sure About not wanting you in my future].
But it's not just about forgetting; he's also a little bit petty (in a fun way!). He hopes his ex has bad luck in love, with the blunt line, "Con la tinta de la verdad escribiré que ojalá En el amor te vaya mal" [With the ink of truth I will write that hopefully In love, things go badly for you]. He's confident he'll be much happier, promising, "Juro que me vas a ver Mucho más feliz que ayer" [I swear you're going to see me Much happier than yesterday]. And to really twist the knife, he says, "Yo seguiré siendo el diez que no superarás Y tú simplemente un cero" [I will continue to be the ten that you won't surpass And you simply a zero]. Ouch! It's a bold, defiant song about moving on and feeling good about it.