Barraco literally means a 'shack' or 'hovel', but in Brazilian Portuguese slang, it's commonly used to mean a 'commotion', 'scene', or 'public quarrel'. It implies a loud, dramatic, and often embarrassing argument or display.
In the song, the lyrics "Pode gritar fazer barraco" (You can scream, make a scene) highlight the singer's defiance. She's telling her ex that no matter how much drama he creates, she won't give in, making barraco a vivid and culturally interesting word.
Have you ever been so done with someone that nothing they say or do can change your mind? That's the powerful feeling behind "Hoje Não!" which translates to "Not Today!"
The singer is putting their foot down with an ex who let them down. They recall a time the ex stood them up and didn't show up for a date ("Lembra daquele bolo que me deu / Daquela noite que você não apareceu"). Now, that same person is shamelessly calling in the middle of the night, trying to come over and explain themselves. But the singer isn't having it. They reject all the ex's desires for intimacy, repeatedly saying, "Vai ficar querendo"—you can keep on wanting. The message is clear and final: "Hoje não, sou mais seu / Hoje não, me perdeu" (Not today, I'm not yours anymore / Not today, you lost me).