It's not the end of the world

Your friend was using your camera and accidentally deleted all of the photos that were saved on it. You don't want to seem too angry, so you say this.

It's not the end of the world.

 This is a phrase to say when something disappointing happens. It means that you're disappointed, but you're not going to get too upset about it. So "It's not the end of the world" is an understated way to say that the situation is bad, but not too bad.