I find the best thing to do is be as honest as I can. I make sure that I explain diabetes quite clearly (only if the other person wants to hear it though!).
If you don't feel comfortable talking about diabetes, others can feel uncomfortable trying to talk about it with you. And some people may seem like they can't be bothered to discuss it with you but maybe they don't know how to tackle the subject with you. I've found that sometimes people feel uncomfortable asking me about diabetes in case they offend me, but I reassure them straight away that I'm happy to discuss it. I don't know how close you are to your colleagues, but maybe you need to just try to explain things openly. I know it sounds quite bad, but if I explain that I can become unconscious if my blood sugars drop too low it sinks in to people that this can be quite serious and that means they are inclined to be a bit more supportive than they may have been. You've mentioned that you have to defend yourself. Explain that if you don't eat when you need to your blood sugars will drop and they will end up having to deal with that. Educate your co-workers into understanding this a bit better. The more info you give them the more they'll understand and therefore support you.
Claire always has good advice. What you might do is leave you diabetes kit with your meter and syringes out on your desk so that people have an opportunity to ask you "whats that". Makes it much easier to bring them around to the topic and then tell them what you want them to know about your situation.