打酱油 (dǎ jiàng yóu)

"打酱油(dǎ jiàng yóu)" literally means "to buy soy sauce," but it's a colloquial way to say someone is just an observer, not involved in the main action. The phrase originates from the casual act of buying soy sauce while running errands, symbolizing a lack of interest or commitment to the main event.

For example:

Wǒ zhǐ shì dǎ jiàng yóu de, bù cān yù zhè jiàn shì.
我只是打酱油的，不参与这件事。
I'm just passing by and not involved in this matter.