Out of the blue!

I use this idiom a lot! You use it when you do something suddenly and unexpectedly.

For example: We were on the bus going to the park, but there was a bad traffic and Tim decided to get off immediately to get in the mall, instead. Everyone was surprised because he made this decision out of the blue.

I decided to go buy Dan's gift out of the blue, because I was exactly walking nearby his favourite store.

Got it?!