Out of the blue

Meaning:

When something happens out of the blue, it happens unexpectedly. When something happens out of the blue, we really do not expect it to happen.

Example sentences:

1. It happened out of the blue.
2. He started singing out of the blue.
3. I don't know why she got upset. It just happened out of the blue.

Example dialogue:

A: Why is Mary laughing?
B: I'm not sure.
A: Did someone say something funny?
B: I don't think so. She just started laughing out of the blue.

Practice:

Can you think of a situation where someone did something out of the blue?

See more examples in this Google search:
It happened out of the blue
(515 results/20Feb05)