I have never liked the idea of injecting through clothes, and as I am happy to get my belly out in public and stab away, it’s never been required of me.
The only time I scurry away to a toilet is if I’m in the company of someone who dislikes needles a lot. There’s a guy at work who went quite a funny colour first time I shot up in front of him! 
I definitely re-use needles though. I just can’t stand the waste if ‘ don’t! Usually not more than 2-3 times a needle, though lancets last forever They are too fiddly to change often…