off the rails

Idioms  

1. In an abnormal or malfunctioning condition, as in Her political campaign has been off the rails for months. The phrase occurs commonly with go, as in Once the superintendent resigned, the effort to reform the school system went off the rails. This idiom alludes to the rails on which trains run; if a train goes off the rails, it stops or crashes. [Mid-1800s]

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Example Sentences

The agency’s rules touch virtually every facet of transportation safety, including regulations that keep airplanes in the sky, prevent gas pipelines from exploding and stop freight trains carrying toxic chemicals from skidding off the rails.

From Salon

Things go off the rails when he says no matter what happens, someone’s getting a ring, which puts tension on the budding relationship.

From Los Angeles Times

"The meeting could easily go off the rails."

From Barron's

The 1974 system went off the rails almost immediately.

From The Wall Street Journal

“She’s not going to change her mind. She doesn’t feel she can take care of a teen, especially now that your mother has disappeared again. She has a son who went off the rails when he was a teenager and she’s not going to go through that again.”

From Literature