I've been smoking in my college's library next to dozens of people and in a class of 40 lol.... all you need to do is breathe into your shirt. I like blowing it and hiding the cig though - people are always WTF.
If there are any hint of problems, I usually inhale and hold it in. There is almost nothing when I exhale.
I should REALLY stop doing it at work though. hehe. shouldn't tempt HR.
But i can't stop by myself!
If you hold your breath for awhile, it greatly diminishes the smoke if not entirely eliminates it. Steam condenses more quickly than real smoke, so you don't have to hold your breath for a really long time. 10 seconds is generally enough. It will give you a hair of a nicotine rush