to blow the whistle, to speak out
Cansou de ser maltratada e botou a boca no trombone.
She got tired of being mistreated and blew the whistle.
The image rests on the trombone, a brass instrument with a loud, deep, far-carrying sound. Long before modern media, such horns were used to make public announcements and call people to attention. To "put your mouth to the trombone" is to broadcast something so loudly that everyone hears — turning a private grievance into a public outcry.
Falando's Idiom Trainer teaches you to recognize idiom meanings and create sentences using them, so you can speak like a Brazilian.
