I think if they aren't Helen Keller they will know you aren't smoking a real cigarette no matter what you are using.
EDIT: The other turnoff for me with 5v devices are charging the batteries. I've yet to see a multi charger for mod batteries. If you have a link to a source I'd be elated. I need enough battery power to get through a day without finding an outlet to charge from or whatever.
My batteries (whether 14500's or cr123a's) last me 6-8 hours on a charge. I carry a spare set in the car always just incase I'm out for 10-12 hours on a particular day so there is no need for charger away from the house. They ususally recharge in less than two hours on my Tenergy or Trustfire charger. Another nice thing about 5 volt batteries, is they only cost about $3.50 and can be recharged 2000 times unlike the small cig style batteries. I get my batteries and chargers from Deal Extreme, Battery Junction or Lighthound. If you use cr123a batteries you can get non-rechargible ones at Batteries Plus to have on hand for an emergency. They have a 10 year shelf life and have lasted me 12 hours of heavy use.