Paisita is an affectionate, colloquial term for someone from the Paisa region of Colombia, which includes the city of Medellín. It's much warmer than just saying 'a person from Medellín'; it's a term full of local pride and identity.
Since this song is a collaboration with Colombian artist Feid and is named after a famous club in Medellín, using paisita is a direct nod to the culture that inspired the track. Learning this word gives you a key piece of insight into the world of reggaeton and Colombian slang.
This is a straight-up party anthem set in a real club in Medellín, Colombia called Perro Negro. Bad Bunny and FEID are trying to convince a girl to dance with them, and they're not subtle about it. The whole song kicks off because she just broke up with her boyfriend, and they think that's a great reason to celebrate: "Vi que te dejaste de tu novio, baby, me alegro / Vamos a celebrarlo en Perro Negro" (I saw you broke up with your boyfriend, baby, I'm glad / Let's celebrate it at Perro Negro).
They're impressed by her wild side, saying she's even more of a troublemaker than they are. The lyrics are full of explicit party details, from dancing and drinking to her pulling out drugs that surprise even them. The flirting is incredibly direct and maybe a little ridiculous. Bad Bunny tells her he wants to get her pregnant on the dance floor—"Un hijo en la disco, voy a dejarte encinta" (A son in the club, I'm going to get you pregnant)—and that if the DJ were a priest, they'd get married right there. It's a song about a wild night out, pure and simple.