Wiktionary
break bad
vb. 1 (context colloquial of an event or of one's fortunes English) To go wrong; to go downhill. 2 (context colloquial especially Southern US and Midwest US of a person English) To go bad; to turn toward immorality or crime.
Usage examples of "break bad".
He hesitated, winding himself up, like a doctor preparing to break bad news.
Pellia rubbed her hands over the bedcover like a small girl who is reluctant to break bad news.
She said it was easier to break bad news to more than one person at a time.
This was the first occasion when she had been sent to break bad news to someone about an accident.
But if the battle looks to be going sour they'll break, and they'll break bad.