I remember standing in a (bouncy) plane toilet, my feet planted backwards and leaning forward with my forehead lodged on the sloping ceiling for stability, syringe cap in my mouth (nowhere else is clean-ish) phial between my fingers, again to avoid dirty surfaces.... that sort of routine used to be common for me. Also totally avoiding touching ANYTHING whilst going to toilets with my kit and NOT putting anything down. Restaurants were often the worst (esp Friday nights), as previously, but made me even more obsessive. On the positive side it made me quite ambidextrous.
For the last 20 plus years I have never moved from where I sit, and though it took a while to get into it, I didn't give a hoot in the end. Nobody ever said anything, and I didn't ever explain it (perhaps once to a mate's kids). I do remember a couple of glares, but I glared back.
In the very old days I had to cook up syringes/needles in pans on a school exchange trip, so it was perhaps more open and discussed in those days, but I would not want to go back to the old kit for sure. Pens are very subtle so I can'T understand anyone making an issue, unless they choose to on principle.
In a perfect world there would be more tolerance and understanding, but that does seem to become less likely as time passes.
xxx