Make a grunt as if to say, "If you don't get it now, you'll be a loser." Then say, "You mean you don't know about the big benefits? Everyone knows already"

When people question why you do things when you are just doing the normal run of the mill things, like they are nosy or super-imposing and you are annoyed, then tell them what they are missing if they don't do the same as you are doing. It will worry them and make them run for the money (with their mouth) for their unwanted curiosity, because they now have to quickly sprint to find out (or beat themselves) for what they have been missing for doing nothing.

Yes, sometimes a grunt and a horrified facial expression speaks more than a thousand words. 

For workplace communication books, visit www.how2talkeffectively.com