Rio de Janeiro,
Used to say that something is a lie, when people are surprised or when something or someone will get in trouble.
"Não acredita nele, ele tá de caô."
"Caô que você ganhou na loteria!"
"Não faça isto, vai dar caô!"
"Don't believe him, he's lying to you."
"I can't believe you won the lottery!"
"Don't do it, you're gonna get in trouble!"