My attitude to injecting in public has always been (since diagnosed a decade ago) that it is as necessary as breathing and I will no more go to the toilet to inject than I will go to the toilet to breathe; after all, I will be equally dead if I stop doing either.
In addition to the problem of injecting in toilets, the point that made me think about it initially was that I was keen not to become conditioned to treating diabetes as something to be kept hidden or to feel ashamed about, which seems to me to cause real problems for the person concerned when that happens. Equally, I'd see it as an essential part of the process of educating everybody else out there.
I always inject through clothes unless I have nothing on, with no diabetes problems that I know about. I would not inject through clothes thick enough to make the depth of the injection uncertain as that could make me miss the fat layer, or if the clothes or needle could be damaged (e.g. plastic mac, leather, perhaps tough and thick jeans) - but that is just common sense.
Over the years I've asked various medical diabetes specialists about it from Consultant level down, and perhaps only 2 out of 6 or 7 have wondered whether there was anything to worry about. I reckon I'm above 12k injections through clothes now.
I have lost several pairs of trousers due to unexpected bloodstains as happens to all of us, so now I inject in my abdoman and wear cheap teeshirts which I can throw away easily.
Rgds
Matt W