Mordío' is a colloquial and shortened form of "mordido," which literally means "bitten." However, in this context, it's used as slang to describe someone who is bitter, resentful, or jealous.
In the song, the lyrics say, "Está mordío' en las redes, tirando pulla" (He's bitter on social media, throwing jabs). This vividly describes the ex-boyfriend's jealousy and frustration, making it an engaging and culturally relevant word to learn.
Jon Z's "Tu Ex" is a super direct and confident anthem about a new relationship flourishing despite an ex trying to stir up trouble. The song tells the story from the perspective of the new partner, who is basically saying, "Hey, your ex left you, you cried, but then you got over it and found me!" He's making it clear that the ex had their chance: "Ya él tuvo su break, ya pasó su break" [He already had his break, his break passed].
The lyrics are pretty blunt and even a bit funny as he tells the ex to back off. He's not shy about saying, "Dile que soy yo ahora el dueño de ese culo" [Tell him that I am now the owner of that ass] and even playfully boasts, "él es medio feíto y yo soy un papi chulo" [he's a bit ugly and I'm a daddy cool]. It's all about how happy the woman is now and how the ex only wants her back because she's with someone new and thriving. Jon Z is basically saying, "You snooze, you lose!" and he's not letting anyone ruin this new love.