As a type 1 diabetic myself, there have been times where I've had to inject insulin in public. I used to go to the bathroom and do it, but I started feeling like I was a drug junkie. That, and some kid gave me this weird look like I was doing something wrong when I walked out of the bathroom stall after injecting my insulin this one time.
Now, I just inject right at the table. However, it's not like I take off my shirt to inject. I just lift a little corner, inject the insulin, and I'm done in 5 seconds. Since I also have to test my blood sugar before injecting my insulin, I try and do that so nobody can really see. That takes all but 5 seconds. 10 seconds total, give or take, and I'm done.