Every day.... I use it against my coworkers when I want actual detailed explainations.  And against random people if I'm not feeling too talkative or just want to hear what they would be saying behind my back otherwise.

And of course, anytime I find myself getting into trouble or trying to bend the rules to my advantage.

Often. Probably daily. For example the people at the major crosswalks in Shanghai who yell at you if you are not standing actually on the curb while waiting for the light to change. And they try to tell you you can't cross if the light has not changed. As if I am incapable of judging when and when not to cross .

i pretend not to speak chinese always to hide the fact  i cant speak chinese

I don't have to pretend. I only know a little Chinese anyway. Most of the time I just end up saying "听不懂."

Yes, whenever a cab driver is talking my ear off and I'm in a bad mood. 

I pretend i dont know any chinese when i have to cut in a freaking long line. just walk up to the front and say i am a foreigner can you help me fill this form out.

i dont pretend. i dont speak chinese. but if i did i would probobly do.

Definitely in a taxi when I couldn't be bothered talking with them especially if they're asking my salary.

Then they can say the word "money money" *rubbing finger motion* then I just say "no money".

all the time... sometimes i dont even say ting bu dong.. i just give them a vacant stare.