Go off the rails

Meaning

to start behaving in a way that not generally acceptable, especially dishonestly: hỗn loạn, hoảng hốt

Example

1. He went off the rails in his twenties and started living on the streets.
2. He went off the rails in his first year at university
3. That would be off the rails in five minutes in an Oxford shop 
4. Ethan went off the rails when he went to the burgh