Big Bang is a kiss-off with a grin. Arde Bogotá spend the first verse listing everything that used to annoy them about someone: "Con tu pelo oscuro, con tu cara larga" (With your dark hair, with your long face), and then the blunt one, "Y esa forma extraña de lamerme el culo" (And that strange way of licking my ass). In Spanish, lamer el culo is the same idea as "kissing someone's ass": sucking up. The verdict on all of it is short and cold: "Daba lástima" (It was pitiful) and "Daba rabia" (It was infuriating).
The chorus is where the title lands. This person never believed in the singer: "Siempre has creído que no iba a durar" (You always thought I wouldn't last), "que no iba a estallar" (that I wouldn't explode). And now? "Y ahora ya soy el Big Bang" (And now I'm the Big Bang). It's a great image, going from someone nobody expected anything from to the biggest explosion there is. The sting is that they hear about it from others, "Me tengo que enterar por los demás" (I have to find out from other people), and the doubter suddenly whispers "te echo de menos" (I miss you). Learner tip: daba is the imperfect of dar, and daba rabia is a really common way to say something made you angry.