No one would object to being, or being called Number One in any language. However, just as no one ever remembers the name of runner-ups, being number two is not so glamorous. In Chinese, well that’s an insult.
To be 二 （er) , that is ‘two’, is to be simple minded, stupid, brainless. It’s a description that is often used as a tease but seldom malicious. You might call yourself 二 (er) for having done something dumb.
One must not confuse being ‘er‘ with being ‘an er’. In Cantonese the later means being the mistress, or ‘the other woman’. There was a chain of soup cafés in Hong Kong called Number Two ‘阿二‘; its inference is that the mistress always has a pot of soup waiting for the Master. The fringe benefit, if you like, or the lure.
What’s the story about being ‘not three, not four’?
Confucius said that a woman must obey her father when she’s at home, obey her husband when she’s married and obey her son when she’s widowed. It is known as the Three Obediences and a code of conduct for women. Further, there are the Four Virtues that all women of good conduct must possess: 婦德、婦言、婦容、婦功. They require a woman to act, speak, look and work as a woman should. Therefore, a woman who is described as ‘not three not four’ 不三不四 is being ‘improper’ and to be despised.
This concept is so embedded in Chinese psyche that today, the term 不三不四 (bu san bu si) – ‘neither three nor four’ is used to describe anything or anyone who is deemed ‘improper’.