The characters are a teenaged boy and his mother. The mom is driving, while the boy is calling out clues from a crossword puzzle that they are completing together to make the time pass.
Teen Boy: “Three Down: River to the Caspian Sea, four letters.”
Mom: “I have no idea.”
Teen Boy: “Thirty-four Across: Knoll, five letters.”
Mom: “Do we have any letters?”
Teen Boy: “Probably starts with M.”
Teen Boy: “I’ll pencil it in. Okay, Thirty-four Across: Doc bloc, three letters, first one is A.”
Mom: “Try AMA.”
Teen Boy: “Twenty-four Down: Beat off. Four letters.”
Teen Boy, very quietly: “Beat … off.”
Mom: “Wow. That’s kind of weird, because ‘beat off’ is a euphemism for …”
Teen Boy: “I KNOW, I KNOW. Let’s just move on to another one.”
Turns out the answer for Twenty-four Down was “fend.” If you doubt the veracity of this anecdote, check out the USA Today crossword for December 18, 2008 (page 7D).