What is That'll Be The Day...?
1.
An expression meaning "That'll never happen". Shortened from "That'll be the day when (insert ubsurd impossible occurence here, such as 'Pigs will fly')"
Bob: I'm gonna kick your butt!
Joe: Haha, yeah, that'll be the day....
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1.
n 1994 - Acceptance by the general population gained by selling out to major record labels
"...maybe your soul you'd sell to ..