This is the meaning of the idiom, WHEN PIGS FLY. We use it to suggest something will very unlikely ever happen or have no chance of happening. These situations will only occur when pigs fly but we know pigs will NEVER fly!
"I'll probably win the lottery when pigs fly." (It's impossible I will ever win the lottery)
"I'll go on a date with that man when pigs fly!"( It's highly unlikely I will go on a date with that man).
Can you make a sentence with this idiom?