As far as insults go in English, calling someone a “dumb egg”, bèn dàn might not really carry much weight. But in China the use of eggs goes beyond the culinary world of fried rice and extends into the linguistic world of name calling.
bèn 笨 means unintelligent and dàn 蛋 means egg. The character dàn 蛋 is also very useful to learn for the purposes of reading a Chinese menu, although most restaurants in China will have pictures of the dishes they serve. Life in China is not always quite as intimidating as many people think.
bèn dàn might seem like a fairly weak jibe in English but in China it can be a serious insult. If you’re in the primary school playground that is, otherwise it’s about as offensive as calling someone stupid. In fact I regularly refer to myself as a bèn dàn.
Similar phrases include huài dàn (bad egg) to describe very naughty people, and my personal favourite hún dàn (confused egg), which is used in a similar way to the word “bastard” in English but is not quite as strong.
You can also shout wán dàn (finished egg) as an exclamation similar to “shit!” in English. If you say wǒ wán dàn le it means “I’m in deep shit”. nǐ wán dàn le (you’re a finished egg) means “you’re in big trouble”.