If the furor over comments that J-pop superidol Kumi Koda made on the radio a few weeks ago teaches us anything, it's to "be careful what you joke about." There are two problems with using humor in public: Either the joke falls flat and nobody laughs, or the topic is beyond the pale and people are offended rather than amused.

The latter problem applies in Koda's case, but the joke was so bizarre that it deserves more scrutiny than it has received. During a conversation on Nippon Hoso's late-night talk show "All Night Nippon," Koda mentioned that her manager, a woman, recently got married. When asked when the manager planned to have a child, Koda said she hoped she would have one as soon as possible. "After a mother turns 35, her amniotic fluid becomes spoiled," the singer said between husky giggles. "True, true! It gets dirty. That's why I want her to have a baby before she turns 35."

The comment didn't elicit shocked silence or the sound of sucked-in air from her interlocutors. "All Night Nippon" is famous for such flippant comments, and by the standards of established comedians such as Beat Takeshi and Sanma Akashiya, who have spent a lot of time on late-night radio, Koda's joke was fairly tame. However, the comment was reproduced on a number of Internet sites, and from there the chat got so poisonous that some people complained directly to Koda's record company, Avex Trax, as well as to companies that use her to sell their wares. The upshot is that Kose Cosmetics and Kirin Beer have canceled ad campaigns featuring Koda, and Avex has suspended PR activities for her new album, "Kingdom," which was released Jan. 31. Despite — or even because of — the negative publicity, the album remains at the top of the charts.