What does "That'll be the day" means?

[Leletup]

Test No. incompl/elem-34 "Responses (7)", question 9

Frank: 'I hear that the Government is going to abolish income tax.'
Jill: '.........'

(a) That is the day!
(b) That could be the day!
(c) That may be the day!
(d) That'll be the day!

Test No. incompl/elem-34 "Responses (7)", answer 9

Frank: 'I hear that the Government is going to abolish income tax.'
Jill: 'That'll be the day!'

Correct answer: (d) That'll be the day!

Your answer was: incorrect
Frank: 'I hear that the Government is going to abolish income tax.'
Jill: 'That is the day!'
_________________________

Hi!

What does "That'll be the day" means?

Thanks!
Leletup

[Alan]

Hi,

This means that you do not believe that day will ever come. In other words you are being sarcastic.

Alan
_________________
English as a Second Language
You can read my ESL story Sea Expressions

[Seanmen]

what does it mean by "sarcastic"?

[Conchita]

[Prezbucky]

A like phrase is "...and pigs might fly..." or "...when pigs fly."

When someone uses one of these phrases, he or she means to convey the unlikelihood of something happening.

George: Evelyn, you're going to be CEO someday!
Evelyn: Yeah, right, and pigs might fly.

OR

Evelyn: Yeah, that'll be the day.
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Billie Jean is not my lover. Hee.

[Seanmen]

Thank you guys.