fly off on a tangent

(verb) to start talking about an unrelated topic

Example Sentences:

The students complained about the professor, because he always flies off on a tangent and starts talking about unrelated things.

While arguing about whose turn it was to do the dishes, Shannon flew off on a tangent and started discussing the laundry.

You are always flying off on a tangent when we’re speaking! Stick to the topic!

From the Blogs:

How to go off on a tangent

Media:

Similar idioms:

1. go off on a tangent
2. fly off the handle
3. pass something with flying colours