Late to the thread, but I'll answer the OP's question:
In class, a Volt.
In a movie theater, my own PV, but I make sure to turn the LED and button lights off, and I only vape when there's loud noise or music. A crackling carto during silence or a dramatic scene can be revealing. I have also altered my movie seating habits by choosing seats closer to the back wall near the projector instead of the middle.
If it's particularly crowded, I always have a Volt with me.
EDIT: I don't travel often so I've never had to worry about air ports and such. Not sure what policies airlines have with vaping. I do know that airplane smoke detectors don't detect "smoke", they use infrared beams that can detect the presence of vapor. So no Nelson "hah hah's!" while traveling by air... Also, not sure how they would handle the liquid...
I don't exhale down my shirt. I just hold it in until there's no vapor left to exhale.
If confronted I follow rules and don't make a scene. Although I would continue to stealth vape during the removal process.