fat chance!

Fat chance! — держи карман шире

Example 1: Bring the trolley back or I'll shoot you now!" "Fat chance," Roland muttered.
(Earth by David Brin, 1990)

Example 2: "Tucker, hush. Mrs. Murphy will be out in a minute — won't you?" Harry leaned over the bin. Mrs. Murphy stared right back up at her and said, "Fat chance."
(Wish you were here by Brown, Rita Mae)

see also
[dream on!]
[in your dreams]
[don't hold your breath]
[fat chance]