Meaning:
Literally meaning “C for morning and A for night,” this originally referred to the recommended practice of using skincare products containing vitamin C in the morning and those containing vitamin A at night before sleep. However, some people have jokingly reinterpreted the term and now they use it to mean “drinking coffee in the morning to keep awake and drinking alcohol at night to fall asleep.”
Example:
A: 你最近忙吗？
Nǐ zuìjìn máng ma？
Are you busy these days?
B: 忙得不行，天天晚上加班，然后早C晚A。
Máng de bùxíng，tiāntiān wǎnshang jiābān，ránhòu zǎo C wǎn A。
I’m terribly busy every day and work overtime into the evening. Then I have to drink coffee to refresh myself in the morning and some alcohol at night to get to sleep.