When the bus starts on it's way the driver says to the hippie, "I can tell you how you can get that nun to have sex with you." The hippie says that he'd love to know, so the bus driver tells him that every Tuesday evening at midnight the nun goes to the cemetery and prays to God. "If you went dressed in a robe and glow in the dark paint mask she would think you are God and you could command her to have sex with you."
The hippie decides this is a great idea, so that Tuesday he goes to the cemetery and waits for the nun to show up. At midnight sure enough the nun shows up and begins praying the hippie jumped out from hiding and says. "I AM GOD! I have heard your prayers and I will answer them, BUT ... first you must have sex with me." The nun agrees but asks for anal sex so she might keep her virginity because she is married to the church. The hippie agrees to this and has his way with the nun.
After the hippie finishes he stands up and rips off the mask and shouts,"Ha! Ha! Ha! I'm the hippie!!"
Then the nun jumps up and shouts, "Ha! Ha! Ha! I'm the bus driver!!"