The nun, surprised by the question, politely declines and gets off at the next stop. When the bus starts again, the bus driver says to the hippie, "If you want, I can tell you how you can get that nun to have sex with you."
The hippie of course 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 to pray to the lord. "If you went dressed in robes and some glowing powder," says the bus driver, "You could tell her you were God and command her to have sex with you."
The hippie decides to try this out. That Tuesday, he goes to the cemetery and waits for the nun. Right on schedule, the nun shows up. While she's in the middle of praying, the hippie walks out from hiding, in robes and glowing with a mask of god. "I am God, I have heard your prayers and I will answer them but you must have sex with me first," he says.
The nun agrees but asks for anal sex so she might keep her virginity. The hippie agrees to this and quickly sets about having sex with the nun.
After the hippie finishes, he rips off his mask and shouts out, "Ha ha, I'm the hippie! "
The nun replies by whipping off her mask and shouting, "Ha ha, I'm the bus driver!"