Resbala literally means 'to slip' or 'to slide'. However, in this song, KAROL G uses the powerful slang phrase "me resbala" which means "I don't care" or "it's like water off a duck's back".
When she sings "Lo que tú digas me resbala" (Whatever you say slips off me), she's expressing complete indifference to her ex's opinion. It's a sassy and empowering way to say that his words have no effect on her anymore, perfectly capturing the song's confident vibe.
This is the ultimate song for when your ex just won't get the message. KAROL G starts by explaining that her old flame is calling her, saying he misses her in bed, but she's completely over it. She declares, "Ahora sólo quiero salir con mi propia squad" [Now I just want to go out with my own squad]. After getting her heart broken, she's not looking for love. Instead, she wants "los mejores tragos y la ropa traída de Dubai" [the best drinks and clothes brought from Dubai]. She's living life on her own terms and doesn't care what anyone thinks. She even warns him that if he thought she was bad before, he should wait for the new version: "Si antes era mala / Ahora viene la nueva versión y más mala" [If I was bad before / Now comes the new, badder version].
Then Bad Bunny jumps in with the same energy, telling his ex to stop stalking him or he'll get blocked on Instagram. He makes it clear she's used up all her chances, saying "Ya tú gastaste todos los strikes" [You already used up all the strikes]. He boasts that he's doing much better single, doing whatever he wants, and isn't interested in true love. He even gives a shout-out to his Colombian collaborator on the track. The message from both of them is loud and clear: they've moved on, they're enjoying their freedom, and their exes need to leave them alone.