二百五 - a stupid person
二 百 五
Lit: two hundred and fifty
Eng: a stupid person/not mature or poised
When copper coins were used in the ancient China, 1000 pieces of copper coins were stringed together as "1 string of copper coins" - used as a currency denomination. Therefore, 500 pieces would make "half a string", indicating "not enough to make 1 string". The term "half a string" is used to refer the people who are not solid or mature enough. 250 pieces of copper coins are only half of the "half a string", which is even less adequate in order to make a full string. So the derogatory term "二百五" is now used to refer to people who are unreasonable, trivial, or stupid.