Payday, usually for government jobs. This phrase dates back to WW2 when soldiers in the U.S. army referred to payday as "the day the eagle shits" in further reference to the bald eagle, a symbol of America.
"Sorry dude, I can't pay you back until the day when the eagle shits"
When an unexpected and nearly impossible event takes place. Usually due to pure luck or the divine intervention of God.
The love of my life left and went back to her own country, and I don't know if I'll ever see her again. But I pray to God each day and when the stars align I hope we'll end up together.