My point exactly, someone will always have something to say no matter how safe you make smoking or vaping. So the best way to handle it is to just tell them... well you can insert whatever you would say here____________
People I worked with referred to it as "huffing his gay pipe." I gave up.
At the end, it's really a matter of where you are when asked upon.
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However, it's completely different if you encounter someone while using it indoors, then you will be most likely facing an individual with a negative mind with responses similar to: "Hey, you are not allowed to smoke here". In this situation, you must come up with an answer that includes the fact that it's legal to use in order to avoid further frustration.
I think sellers should not make any claims saying that it is legal to use indoors. Because at the end, it's really the decision of the property owners.
E-cigarettes do have an aroma, and it does produce vapor that can possibly set off fire alarms. Exhaling any sort of vapor indoors really conflicts a standard human logic and could have a negative impact on how the government will view such devices in the future.