I have been told to inject elsewhere when out and about, some people are needle phobic so I can see why they would be uncomfortable, but I would expect people to be mature about it and not make a scene.
I generally ask if everyone I am with is OK if I inject when i need to, and if someone has a problem with it I go to the bathroom or round a corner so I don't upset anyone. I agree it should not be the diabetics responsibility to cater for other peoples issues but I suffer from a phobia and I appreciate people not triggering it so I see it as give and take
I have been dragged out of a club by security for injecting in the bathroom once, I did point out dealers are unlikely to distribute illegal drugs in Novo pens. After showing them
http://en.wikipedia.org/wiki/Insulin_pen on my phone they let me go, I tried to get free drinks for the night for the hassle but it didn't work
I guess the answer to these issues is education, let people know what you do and why it is necessary, and let them decide what to do.