I drip fill my cartos in public all the time.
Like Petrodus said, I don't really care what someone else thinks.
On the positive side some people have seemed to overcome their own shyness when i do this, and ask about e-cigs. The comments are usually along the lines of.. hey is that one of those electric smoke things?!
Allot of people are very positive in their reactions, and I steer them WELL clear of the mall/radio add stuff. This is the most common seconday reaction. Oh like XYZ in the mall?! No, no, no, NO!
Regardless, the overall reactions are typically really good, especially when they hear about the benefits, no burning, good smells, less money, no carcinogen stuff. Some people ask to 'smell' the bottle and depending on who/where I may let them get close for a whiff (I usually vape things like french toast/thin mint/etc). This actually seems to get people more excited than the tobacco flavors.
In the end, no shame, no guilt, drip!