I'm here to get some soy sauce .
Lol...I have no clue what that means, but that might make it even funnier.
Some actress got their naked sex picture taken by an actor and spread publicly .
The Chinese TV interviewed several passerby : How do you feel about this news event ?
One guy said : Hell , what do I have to do with it ? I'm just come to the store to get some soy sauce . (Literally, he was getting soy sauce) .
So, the phrase is to describe those who doesn't want to express their idea at this point , but just here to observe .