Labia is a popular colloquial term for 'smooth talk' or the 'gift of gab'. It refers to the special skill of using charming and eloquent words to persuade, flirt with, or sweet-talk someone.
In the song, Bad Bunny sings, "Yo no voy con labia", which means "I don't do smooth talk". He's saying he's direct and honest about his intentions, warning the other person not to expect romantic sweet-talk from him.
In "La Santa," Bad Bunny and Daddy Yankee are dealing with a classic problem: a casual hookup that's getting complicated. The song is a direct message to a woman who knew the deal from the start but is now catching feelings. Bad Bunny is blunt about it, saying, "Te lo dije que esto era pa' jugar / Que no te podías enamorar" (I told you this was just for fun / That you couldn't fall in love). He reminds her that neither of them is innocent—"Tú no eres una santa, ni yo soy un santo" (You're not a saint, and I'm not a saint either)—and that she enjoys the party lifestyle just as much as he does.
He's not trying to be a romantic hero here. In fact, he's completely against it. He makes it clear that "El romance no es mi área" (Romance is not my area) and that he always dodges Cupid's arrow. The reason? He keeps his heart "dentro de la nevera" (inside the fridge), saying it's cold and he doesn't trust anyone. It's a very straightforward song about setting boundaries in a physical relationship and pushing back when one person tries to change the rules.