Fat chance

Fat chance: Algo que dificilmente vai acontecer / algo com chances reduzidíssimas / pouquíssima possibilidade

“I was hoping they might have forgotten my offer. Fat chance!”

“Fat chance he has of getting a promotion.”

“ You think she'll lend you the money? Fat chance!”

(http://www.macmillandictionary.com)

Fat chance

Fat chance: pouquíssima chance, sem chance,impossível ou quase

"Maybe they’ll invite you to go with them." "Fat chance!"

( www.dictionary.cambridge.org)