"Ways of the World" joke

One night a woman is driving down a country road when her car breaks down. Fortunately, there's a farmhouse nearby so she asks the farmer if she can stay there for the night.
"Well," the farmer drawls, y'all can stay here but don't go messin' with my sons, Billy-Bob and Earl."
Looking through the screen she's able to see two young men in their early twenties. "Okay," she says.
After they had all gone to bed for the night the woman starts to get a little horny just thinking about the two young men in the next room. So, she sneaks into their room and says, "Hey boys, how would you like me to teach you the ways of the world?"
"Huh?" ask the puzzled young men.
"There's only one condition," she says. "I don't want to get pregnant so you have to wear these rubbers. She then puts them on the boys and the three of them go at it all night long.
Thirty years later, Billy-Bob and Earl are sitting out on the front porch and Billy-Bob says, "Earl, 'member that woman that came by here 'bout thirty years ago and showed us the ways of the world?"
"Yep, I reckon I do," replies Earl.
"Well, do you care if she gets pregnant?" asks Billy-Bob.
"Nope, reckon I don't," replies Earl.
"Me, neither," Billy-Bob says. "Let's take these dang things off."