I was out with my therapy group on a shopping trip a couple of weeks ago. We ended up getting ice cream and sat outside with the ice cream to eat it in the little bit of sun we had that day. I told everyone I had to inject and they were very encouraging. "Do what you gotta do! Nobody's business but you're own."
I tried to be as discreet as possible using my shoulder bag in front of my lap because I'm worried about people with needle phobias more than I am about keeping it a secret, but I didn't feel hugely uncomfortable - mostly a little uneasy because it was a new experience. I've only been on insulin for 4 months and not yet had many instances where I was outdoors/in public for an injection, but I vowed to myself from the start I wasn't going to hide it, I'd just be discreet because I know phobias are no joke. If someone sees it while I'm being discreet they were obviously prying and then it stops being my problem!
I do have a history with getting hassled out in public because I eat. I'm fat and some jerks really don't hold back on making their opinion known that they find me disgusting when I eat something quick and not too healthy while walking/biking (nothing like an ice cream cone while biking through the German and Dutch landscape lol). I was 15 the first time this happened and it's happened often since and left a mark. It makes eating in public something I avoid in general and sometimes I feel an injection will be 'another' prompt for harassment like this ("she's so fat and unhealthy she has to take insulin from self-induced diabetes!"), so I do feel some anxiety about it.
Buuuuuuuut jerks who are that rude are generally miserable shits without compassion or a single grain of humanity in them. They usually look like the type that hurt defenseless animals, so I try to remember that their opinions aren't worth fussing over even if it's hard at times. I'm beautiful and taking care of my health around the clock, I'm allowed a treat when I'm out and about like anyone else. They don't know how much time I spend trying to be healthy even if I don't fit the physical ideal of health.