Mine are a few that have been mentioned here.
People recomending a new person to start with a mod. I think a good start is a Joye Ego with MAYBE a LR atomizer at the most.
People that ask me for a lighter or to bum a ciggarette when I am clearly vaping.
People that say, "Why smoke an electronic cigarrete? You might as well just quit cold turkey if you smoke that."
When people ask, "What is that?" and I tell them for them to say, "So its a fake cigarette... what is the point, that is just plain stupid...". Or simply... "Is that one of those stupid fake electronic cigarettes?"
When People see me smoking an E-cig and decide to switch over from an analog. They dont ask about what model I have and buy somthing like a Blu and dont know about nicotine level, other models, etc and get upset about wasting 80 bucks and blame you for their faults because they still smoke cigarettes.
When people push/recomend highly expensive mods on people when they have limited money and think that because they are expensive, the are superior.
When people believe that because they own a specific mod it is the best and they only recomend those.
When people ask on DIY about what percentage of flavor they say, "try it yourself" instead of "I do them at 15% so start from there".
When people look at you as if you are smoking a real cigarette and give you the "evil eye look".
When people start coughing or cleaning their throat when you vape near them.
When I ask for a cigarette on the rare ocasion from a friend and they say, "You have an E-cig, smoke that? Whats the point of smoking that if you are going to smoke a cigarette, you might as well not even smoke a E-cig at all!"
Those are the ones that I can think of at the moment. I am sure there are more but since they dont come to mind they probrobly dont bother me as much.