In American English, when someone responds to you by saying, "In your dreams!" does he mean that you're actually dreaming?
A: Guess what? This weekend, I caught a fish this big.
B: No way.
A: Yeah, It was huge!
B: In your dreams! There's no way you caught a fish that big.
"In your dreams" is a different way of saying, "I don't believe you" or "there's no way that's true."
It is a way to tell people that you think they are making up a story.
And this phrase is used in a playful manner, usually with a smile.
"In your dreams!"
"In your dreams!"
"In your dreams!"
And that's English in a Minute.