I must say I'm really shocked to hear about peoples experiences. When I was first diagnosed, I must say I was shy, and didn't want to do it in public, but as time has gone on (17 years) I've stopped caring. Now I usually inject where and when I need too, regardless of situation. I must be very lucky as I have never had anyone stop me or complain having done it in public, and I've done it on buses, tube station platforms, and at the table at conferences. I tend to do it through my clothes in the leg or stomach with an insulin pen (nurses would not be impressed if they knew that!) so maybe no one has noticed, or the pen makes people realise what it is.
What makes me laugh about the whole confusing it with being drug addicts thing, that people seriously think that someone is going to inject an illegal substance in front of a bunch of people in a restaurant! What is the likelyhood!? Plus I've never heard of a drug addict using a pen! Some people need to use their heads more, they are just ignorant!
I say don't let people get you down, you can't help you are diabetic, and as people have said previously, it's like taking a normal drug, just in another form of delivery. Do what suits you, forget what others think. Also I'm pretty sure that If people at work complain and insist you do it in the loo, well that's discrimination and you can do them for that.