that'll be the day!INFORMAL
This page is about the conversational phrase that'll be the day!
You can say this if you don't think something will ever happen or become true.
- "I'm going to quit drinking and smoking and exercise more."
"That'll be the day!"
- Adam said, "In the free-market economy, workers will also get rich," and Karl scoffed and said, "Hah! That'll be the day!"
You can say "That'll be the day!" if you think something
Contributor: Matt Errey