lately when I have wanted to go up to people (usually much older though!) and whisper a polite warning--such as last week with the woman in souq waqif wearing a halter top. I have also always minded my own business.
You would think that people would know to be conservative in a Muslim country, but obviously some people have no clue. Too bad we can't be given the DO's and Dont's for living in Qatar on a small card when we go through immigration after getting off a plane.