I am always tempted to shout back "Do you jackholes really think that's the way to get a woman interested in you? Pray to the Virgin you're not still one when you die." But of course I never say anything, because I'm technically at work plus I don't feel like getting attacked by horny losers with nothing better to do that harass women in the middle of the day.
Maybe I can make a sandwich board to wear when I must walk the downtown streets: "Wanna get AIDS? Ask me how." Except that would only deter people who a) know how to read and b) aren't HIV-positive already. I'm not convinced that my onroad admirers meet both qualifications.