Meaning of (A) FAT CHANCE (OF STH / DOING STH) in English

(A) FAT CHANCE (OF STH / DOING STH)

( informal ) used for saying that you do not believe sth is likely to happen :

'They might let us in without tickets.' 'Fat chance of that!'

Oxford Advanced Learner's English Dictionary.      Оксфордский английский словарь для изучающик язык на продвинутом уровне.