So there's this nun, and she gets stranded a looooooong way from her convent (don't ask how, it'd only spoil the story). After weighing up the situation, she reaches the conclusion that the only way to get home is to hitch a lift. So she stands at the side of the road with her thumb out, waiting for someone to stop.
Shortly thereafter, a car draws up beside her, and the driver winds down his window and asks where she wants to go. Having established that her convent is in the general direction of his own destination, the driver opens the door for her, and in she gets, whereupon they start off on the long drive conventwards.
After a few hours drive, they reach a service station, and the driver proposes stopping there for a bite of breakfast. "Oh, no,"says the nun. "Because of my vow of poverty, I have no money, so I couldn't possibly buy myself breakfast." "No problem," says the driver. "I'll buy you breakfast ... but it'll cost you, if you know what I mean ..."
So they have breakfast and drive on. An hour or two further along, feeling the pangs of conscience, the driver sheepishly asks, "What will you tell the Mother Superior when you get back to the convent?" The nun says, "Well, I shall simply tell her that I accepted a lift in good faith form what turned out to be a wicked man who had his way with me twice."
"Twice? says the driver. "But it only happened once!"
"Oh, I know," says the nun ... "But we are going to have lunch, aren't we?"