This is a serious matter; let's not joke about it.

这是正经事， 可别打哈哈。

《新英汉大辞典》

You should not joke about his mistake.

你不应该取笑他的错误。

youdao

John seemed to be off his feed, he did not joke and laugh with the others.

约翰似乎有心事，他不跟别人说说笑笑。

youdao

But it was not a joke. NASA found seven normal, everyday supermen in a group of five hundred candidates.

VOA: special.2009.06.10

That seems like a bad joke,but if the body theory is right, it's not a joke at all.

又是一个冷笑话，但如果肉体主义者是对的，这就不是开玩笑了。

耶鲁公开课 - 死亡课程节选

Unfortunately, it didn't work very well because people started bickering in his town and the New Harmony became kind of a joke-- it was not a harmonious community.

但不幸的是，这座村落发展得并不顺利,矛盾争执丛生,新和谐村成了笑谈-,因为已经无谓和谐了。

耶鲁公开课 - 金融市场课程节选

That is, that the joke is one to be shared with said editors and the readers, not a joke upon the editors and the readers.

FORBES: Best Letter to the Editor of the Year

It left me suspended in a bad joke in which a living man inexplicably becomes two pints of dust and everyone acts as if this were not a joke at all but, rather, the most reasonable thing in the world.

NEWYORKER: Dead Man Laughing

But given that Casey lives in Arizona and has an American girlfriend and coach, this was clearly a joke, perhaps not the funniest joke, but worth nothing more than raised eyebrows from the American camp.

BBC: Candid Casey eyes fresh start