Speaking on my behalf, I am not qualified to tell you what you are and are not. With that I can tell you how I am in similar situations.
If I am bothered by something it will sit inside and build, I am not very good at releasing these things other than exploding. I have done this to customers, people I work with and people in charge. I get to a point where nothing matters more than me getting out what I need no matter what others may think. In my work though there are only specialists so replacing an employee isn't as easy as a supermarket. I also don't have feelings so much of who I am but definitely on what others perceive. My own thoughts and mind is my worst enemy in these times. If I feel offended or even worse disrespected I cannot stop from getting to that point where most will pull away from. Guess this is one of the traits that makes a difference in some of my issues compared to others. I too am not the best social person as I do offend people all too often and wind up embarrassing my wife. The N part of me is always striving to prove something and that is not a good thing. For you there are probably many great tactics to use so that the people who ask stupid questions (which there will be many) and comments you can be armed with answers that will make your inner self feel good. The sugar guy for instance, a good reply would of been "well feel free to empty the packets into the jar if that makes you feel better". Or direct him to a manager to listen to his concerns if speaking back isn't your thing. I know my N side always wants to be on top. The one above wrote about using narcissism as a strong point. I do this as second nature but with that also brings a side that all the nons speak of. That is the dark, misunderstood by all side. The side that could cause you to lose your job. My narcissistic pride has never allowed me to think as a proper functioning adult, especially when i'm bothered. When I show this side it's never good! I suppose you can also keep it in and deal with it if you can, just not something I can do. Maybe one day I will be able to. I guess that's the magical question, how??