He was showing that he knows nothing about Glucagon OR Heroin, for that matter, when he made that comment. Glucagon gives no 'high' like what illicit drug users get when they take them, doesn't change your behavior, etc. It is not addicting, either. All it does is to stimulate your liver to dump some of its reserves of emergency sugars to help you recover from a severe hypoglycemic reaction. I have had my husband use Glucagon on me a number of times in the past to help me when I was severely hypoglycemic, and I truly believe it can be a real life-saver. There are GOOD drugs that when used properly help us, and there are 'bad' drugs that destroy people. Nobody with any knowledge of them would compare the two. If he is offensive, ignore him, but if your concern is that some of your friends may start to think that you are using 'bad' drugs, then you may want to ask your teacher if you can educate your classmates. Most have absolutely no idea what type 1 diabetes is, for all of the media publicity is about type 2 diabetes, which has different causes and treatments. I find that most people are fascinated to learn that type 1 is an autoimmune disease, and that it is related to other autoimmune diseases like thyroid disease, rheumatoid arthritis, and Lupus.
Not a stupid question at all...no matter what your age, people will always have something to say about diabetes. Most people have no idea what they're talking about and, moreover, no concept of how hurtful simple uneducated comments can be. You have every right to feel frustrated by his careless and insensitive "jokes." However, you also have to let these things roll off of you. Explain to him once that glucagon is an important part of your health and well being in the event of severe low blood sugar, hopefully he will be mature enough to accept this information with respect. If he does not, then his opinion really isn't worth your time or energy.
P.S. At 14, boys say just about anything to get a girl's attention and reaction, simply ignoring him might be just what he needs ;)
Don't worry about that hun just make sure he can give you an injection. He will understand later kids are stupid they only know what they find out and #1 what we teach them. Don't worry about his perception just teach him how to respond to a crisis things will take carte of themselves later.