The Idiom Attic - a collection of hundreds of English idioms, each one explained.
The meaning of "vatican roulette"
" Vatican roulette "
Meaning:
The rhythm method of birth control.
Example:
It's a real dilemma for my wife and me. I know Bridget is a Catholic and that condoms aren't allowed, but I don't want kids yet and Vatican roulette is just too risky for me.