“Getting soy sauce"
This phrase is used in the same way as "it's none of my business" and "no comment".
There's actually a rather entertaining story behind it but it takes a little explaining so bear with me!
Edison Chen is (was?!) a very popular, famous Hong Kong-based actor, singer, model, fashion designer who got into a spot of bother in late 2008 after 465 pictures of him having sex with different well-known Chinese actresses were leaked after his computer went in for repair.
There was a huge backlash in China resulting in substantial news coverage of the event, focusing on people's outrage and condemnation of the leaked photos.
A Guangzhou TV station took to the streets to canvass public opinion but when asked about the scandal, one man responded with "关我屌事，我出来买酱油的!” which means "I don't give a f***, I'm just out buying soy sauce!"
Netizens fell in love with this guy and his comment took online chatrooms by storm - what's the latest happenings in Hollywood? Hell, I'm just out buying soy sauce!
＝"It was nothing to do with me - I was just out buying soy sauce"