脑子瓦特了 (nǎozi wǎtè le) — Brain has short-circuited; completely lost...

Example Usage

你居然买了十双鞋？脑子瓦特了吧！

You bought ten pairs of shoes?! Have you lost your mind?!

Cultural Context

Wǎtè comes from 'watt' — the unit of electrical power. Saying someone's brain has 'gone to watt' means it's burned out or malfunctioning. Used both as light teasing and genuine disbelief.