go off the rails
idiomPart ofrail
go off the rails — idiom
1. To start behaving in an unacceptable or strange way, often due to problems.
1.idiom
Definition
To start behaving in an unacceptable or strange way, often due to problems.
Example
After losing his job, Brian went off the rails and started drinking heavily.
The project went off the rails when the main investor withdrew.