1. slang A method of birth control in which heterosexual partners do not engage in sexual intercourse while the woman is ovulating; more commonly known as "the rhythm method." An allusion to contraceptives being banned within the Catholic ideology and the fact that the effectiveness of such a method is as much a gamble as playing roulette. In this day and age, and with four children already, I find it mind-boggling that you and Sarah would be playing Catholic roulette to keep from having another baby. My periods have always been unpredictable, so I've never trusted Catholic roulette as a potential method.
2. slang A method of birth control in which a man withdraws his penis from his partner's vagina before ejaculating; more commonly known as "the withdrawal method" (technically called "coitus interruptus"). We got so caught up in the moment that I didn't bother asking if he had a condom, so I just told him to pull out before he came. Well, suffice to say that we lost that game of Catholic roulette.
3. slang Heterosexual intercourse in which no birth-control methods are used at all. Why on earth would you not use a condom, dude? If you go playing Catholic roulette with every girl you hook up with, you're going to end up with a baby in your arms before you've even graduated college!