A German couple, 30- and 36-years-old respectively, went to a fertility clinic after eight years of marriage to find out why they weren't having children, only to discover that they didn't understand what sex was. Oops!
"When we asked them how often they had had sex, they looked blank, and said: 'What do you mean?' We are not talking retarded [Edit: Their words not ours.] people here, but a couple who were brought up in a religious environment who were simply unaware, after eight years of marriage, of the physical requirements necessary to procreate," said a clinic spokesperson. [Straight Dope]