I have this weird but reproducible thing that I can see my breath for less than a second even in hot/humid weather. The key to do that is to pop my ears - I have to do that often, it's like I'm on a flight, not sure why my ear is that way... Anyway even if I just try to force more air into my mouth, keeping it flexed (not blowing it up like a balloon)... At the moment I open mouth and let the air out I can see it. I noticed it on a hot day in the car, against the darkness of the dashboard I could see the vapor. Also just about anywhere, anytime. It's barely visible though. My friend can see his breath during or after rain (!)... I think it has something to do with pressure and relative humidity - but then why does it work in very humid weather too, also in the bathroom? If I breath out normally it does not happen at all! I'd like to know the scientific explanation (and if it's normal or there is something wrong with me).
The relative humidity of air is pressure dependent. Your method of popping your ears involves increasing the pressure of the air in your mouth. And if you sufficiently compress a volume of air that has a high relative humidity, you can increase the air's relative humidity beyond it's saturation limit, which causes the water vapor in the air to start to condense, producing a visible mist.
You can find videos and descriptions of this phenomenon by googling "mouth mist trick".