Meaning:
Originating from Shanghai dialect, “瓦特” is used to replace another word with the same pronunciation in the dialect, which should be “坏掉,” meaning “broken.” It’s often used together with “brains,” as in “脑子瓦特了” (literally, brains are broken). Because the Mandarin pronunciation of “瓦特” reminds people of the English word “water,” and a previous saying “脑子进水” (literally, water entering the brain) also means “stupid, crazy, insane,” Chinese netizens have immediately embraced the new term and used it in a similar way.
Example:
A: 你做过最尴尬的事情是什么？
Nǐ zuòguò zuì gāngà de shìqíng shì shénme？
What’s the most embarrassing thing you’ve ever done?
B: 上中学的时候暗恋一个男生，鼓起勇气给他写了一封很长的情书，但是第二天脑子瓦特了，把情书夹在作业里交给老师了。
Shàng zhōngxué de shíhòu ànliàn yīgè nánshēng，gǔqǐ yǒngqì gěi tā xiě le yīfēng hěnzhǎng de qíngshū，dànshì dìèrtiān nǎozǐ wǎtè le，bǎ qíngshū jiá zài zuòyè lǐ jiāo gěi lǎoshī le。
I had crush on a boy during middle school and finally plucked up my courage to write him a long love letter. The second day, in stupidity, I submitted the love letter to the teacher because I had tucked it inside my homework.