I don't know the affect of injecting in the arms. I know the absorption could be faster in the legs if you exercise immediately after injections. I wander if injecting in the arms and then pretending to be a windmill could have a similar affect.
Probably best to try in a safe environment (e.g. at home) and see how it affects you
Why do you do a clinical procedure in a toilet?
Unless I wear a dress, I was always able to lift by shirt, jumper, ... and stab my tummy. I did this at my desk opposite a colleague for over a year before he noticed. People are less interested in diabetes than we think.
If you want some privacy, could you ask your employer to provide a more hygienic environment?