Say what you like about Sarah Palin, but if you happen to be David Letterman, or any other member of America's liberal media elite, then it's an extremely bad idea to go cracking jokes about the sex life of her teenage daughters.
The veteran chat-show host has been forced to make not one, but two on-air apologies after a comic monologue making fun of the Alaska Governor and her colourful family life spectacularly backfired.
"It was a coarse joke, a bad joke," a contrite Letterman admitted during Monday night's edition of The Late Show. "The joke, really, in and of itself can't be defended... I'm sorry about it, and I'll try to do better in the future."
Trouble had been brewing since last week, when Letterman devoted a segment of his programme to topical gags about a visit Palin had made to New York with her husband, Todd, and 14-year-old daughter Willow.
After relatively innocuous jokes about a trip to Bloomingdales, Letterman moved on to the Palins' trip to a New York Yankees baseball game. "There was one awkward moment during the seventh inning stretch," it went. "Her daughter was knocked up by Alex Rodriguez," the Yankees star with a famously voracious sexual appetite.
Conservative viewers were not amused, since it soon emerged that Willow, and not Bristol, had been in the crowd. Within hours, the Palins accused Letterman of making "disgusting" jokes that made light of the sexual exploitation of a 14-year-old girl.
"Hollywood and New York entertainers have a long way to go in understanding what the rest of America understands," claimed Mrs Palin, who added that such jokes "contribute to the atrociously high rate of sexual exploitation of minors by old men."
The row snowballed, and though Letterman issued a half-baked apology on Friday, outraged supporters of Mrs Palin threatened to picket his studios.
Cynics wondered if both Mrs Palin, mulling a presidential bid in 2012 and Letterman, whose ratings recently overtook rival Conan O'Brien, had an interest in stirring up a dispute.
However CBS, the broadcaster of The Late Show, was very soon disabused of that notion, when advertisers like Embassy Suites, the hotel organisation, began pulling out of the show.
Letterman's second apology lasted eight minutes. It was humorous in tone, and stressed that he had intended in his original joke to portray Bristol Palin, 18, rather than her younger sister.
Yesterday, Palin accepted it "on behalf of young women, like my daughters, who hope men who 'joke' about... sexual exploitation of girls will soon evolve".