Idiom- When Pigs Fly - Idioms and what they mean?

Idiom- When Pigs Fly!

Meaning-

Something that will never happen

Impossible

Highly unlikely to happen

Sentence-

I asked my boss if I could go on a two month vacation, he said yes, when pigs fly!

I think he’ll pay you back your money – when pigs fly.

“when pigs fly” is  common in America.