All languages have their own set of insults and Chinese is no different.  My favorite Chinese put downs involve questioning the full functionality of the other person’s brain.  Brain insults in the Chinese language come in a wide variety.  You could tell your friends that they “were kicked in the brain by a donkey” or you could also suggest that that possibly they do silly things because their “brain has water in it” insult.  If you learn all the brain insults from this Chinese slang lesson, you will never be at a loss of words to accurately describe a complete moron using the Chinese language the way the same way the locals do it.  This is a skill that will come in handy for any foreigner living in China for any long period of time.    

脑子有问题-nǎo zi yǒu wèn tí-Something wrong with the brain

Literal Translation-Brain has problem

当然，他做了一个愚蠢的决定。他脑子有问题。

dāngrán，tā zuò le yígè yúchǔn de juédìng。tā nǎozi yǒu wèntí。

Of course he made a stupid decision. There is something wrong with his brain.

脑子有毛病-nǎo zi yǒu máo bìng-Something wrong with the brain

Literal Translation-Brain has illness

你一定是脑子有毛病才会跟老板说那话。

nǐ yídìng shì nǎozǐ yǒu máobìng cái huì gēn lǎobǎn shuō nà huà。

You must have something wrong with your brain for saying that to the boss.

脑子坏了吧？-nǎo zǐ huài le ba-Is your brain broken?

你怎么能那样想，你脑子坏了吧？

nǐ zěnme néng nàyàng xiǎng，nǐ nǎozǐ huài le ba？

How could you have thought that? Is your brain broken?

脑被驴踢了-nǎo bèi lǘ tī le-Stupid or crazy. Kicked in the brain by a donkey (Adj)

他大概是脑被驴踢了，才会这么蠢。

tā dàgài shì nǎo bèi lǘ tī le，cái huì zhème chǔn。

I think he was kicked in the brain by a donkey and that is why he is such a moron.

脑子被门夹了-nǎo zi bèi mén jiā le-Brain slammed in the door

他小时候脑子被门夹了，所以才会是个猪头。

tā xiǎoshíhòu nǎozi bèi mén jiā le，suǒyǐ cái huì shì gè zhūtóu。

He had his brain slammed in the door as a kid, that’s why he is such a moron.

脑子进水-nǎo zi jìn shuǐ-Water in the brain

你怎么这么像个白痴？你脑子进水了吗？

nǐ zěnme zhème xiàng gè báichī？nǐ nǎozi jìnshuǐ le ma？

How could you be such an idiot? Did you have water in your brain?

脑子养鱼-nǎo zi yǎng yú-Fish in the brain

他不记得问题是因为他脑子养鱼。

tā bú jìde wèntí shì yīnwèi tā nǎozi yǎng yú。

He doesn’t remember the question because he has fish for brains.

脑子里有屎-nǎo zǐ lǐ yǒu shǐ-Shit in the brain

他脑子里有屎，才会总觉得自己很伟大。

tā nǎozǐ lǐ yǒu shǐ，cái huì zǒng juéde zìjǐ hěn wěidà。

The reason why he thinks he is so great is because he has shit in his brain.

脑子短路-nǎo zi duǎn lù-Brain short circuit

我真不该说那些话。我觉得我是脑子短路了。

wǒ zhēn bùgāi shuō nàxiē huà。wǒ juédé wǒ shì nǎozi duǎnlù le。

I never should have said that. I think my brain short circuited.

脑子不好使-nǎo zi bù hǎo shǐ-Brain doesn’t work well

他总是犯错误是因为他脑子不太好使。

tā zǒngshì fàn cuòwù shì yīnwèi tā nǎozi bú tài hǎo shǐ。

He always makes mistakes because his brain doesn’t work too well.

脑子秀逗-nǎo zi xiù dòu-Something wrong with the brain

我除非是脑子秀逗了才会去冰冻的河里游泳。

wǒ chúfēi shì nǎozi xiùdòu le cái huì qù bīngdòng de hélǐ yóuyǒng。

Only if I had something wrong with my brain would I swim in a frozen river.

脑子转不过弯-nǎo zi zhuǎn bù guò wān-Brain can’t think quickly

Literal Translation-Brain cannot turn the corner

别人听到笑话都笑过五分钟后他才笑。他脑子转不过弯

biérén tīngdào xiàohuà dōu xiào guò wǔfēnzhōng hòu tā cái xiào。tā nǎozi zhuǎn bù guò wān。

He laughed at the joke five minutes after everyone else. His brain doesn’t think very quickly.

脑有屎-nǎo yǒu shǐ-Shit in the brain (Adj)

他脑有屎，听不懂你的话。

tā nǎo yǒu shǐ，tīng bù dǒng nǐde huà。

He doesn’t understand you because he has shit in his brain.

榆木脑袋-yú mù nǎo dài-Wood in the brain (Noun)

嗨，“榆木脑袋”，你先检查过电源有没有插上吗？

hēi，"yúmù nǎodài"，nǐ xiān jiǎnchá guò diànyuán yǒuméiyǒu chāshàng ma？

Hey “Wood for brains”, did you check if the power was on first?