It means you are still stifling polite when ruddy-cheeked Martin from accounts makes his way over to you, brandishing a forlorn looking sprig of mistletoe. 'Um no thank you, Martin...'.  However were you more emotionally lubricated, you could probably find two far more effective words to use on Martin.  

Sure, no problem, that's fine. The words have tripped out of my mouth before you can say nervous breakdown. WTF. 

We know the feeling well, so accustomed are we to it. It leaves un-drunk cups of tea, unshaved legs and unread books in its wake. The feeling that we must be all things to all people...but ourselves it seems.