Fiddling with little liquid tanks and/or the innards of a box mod half-hidden beneath a blanket, while nervously looking about to see who might be looking at you trying to get in a stealthy nic fix vape, might, just might, stress out, say, an air marshal -- if he were to catch a glimpse, and didn't know much about e-cigs. They are likely well trained to spot such behavior. Box mods particularly do kind of look like little liquid bomb contraptions.