From Longman Dictionary of Contemporary Englishin your dreamsin your dreamsspokenIMAGINE used to say in a rude way that something is not likely to happen ‘I’m going to ask her to go out with me.’ ‘In your dreams!’ → dream
Examples from the Corpus
in your dreams• Believing in your Dreams is a powerful magnetic force!• No doubt he was studying the Cabala in his dreams.• He was very frightened of the spirits and they ran after him in his dreams.• I know they will come back to haunt me in my dreams.• He was a prophet too, and spoke to men in their dreams.• The gods often spoke to men in their dreams.• A pirate who might have been a Susan in his Dreams.• Her spine twisted; in her dreams she twisted, turning toward that clearing again, again.• "I can beat you, no problem." "Yeah, in your dreams." 