Meaning:

打酱油 (dǎ jiàngyóu) to buy some sauce, to be a bystander

Usage:

“打酱油”原指孩子大了可以帮家长做一些家务事。网络语境中，表示某人对话题漠不关心，或者在一项活动中没有起到任何作用。

“打酱油” originally referred to how kids, when they grow up, can help their parents with housework. When used on the internet, it means that someone is indifferent to a topic or can change nothing during an event.

Examples:

1. 麦蒂在马刺队一直扮演着打酱油的角色，但是他对此并不在意。

    Màidì zài Mǎcìduì yīzhí bànyǎn zhe dǎ jiàngyóu de juésè, dànshì tā duìcǐ bìng bú zàiyì

    McGrady played the role of bystander on the Spurs, but he doesn’t care.

2. 等你结婚的时候，我儿子都能打酱油了。

    Děng nǐ jiéhūn de shíhòu, wǒ érzi dōunéng dǎ jiàngyóu le

    When you get married, my son can help with chores.