I'm type 1 diabetic and have been I guess for many years now. When I personally take injections, I am always aware that others may find watching this disturbing. Lets face it, as a non-diabetic, its not every day you see someone stick a needle in themselves. So I try do do it as much as possible in a modest and respectful way. Especially somewhere like a restaurant, where frankly people don't want to lose their appetite.
Some people I have seen unfortunately make a point injecting in a "you got a problem with this?" kind of way. Its not the fact that you are taking an injection thats likely to cause problems, but more the way you are taking it.