When I was taking insulin using a vial & syringe or a prefilled pen I didn’t feel the need to go to the restroom to do it. I could use my abdomen, my upper arms, my thighs with a bit of discrete adjusting of my clothes. I even went through my clothes if I was fairly certain of the area I was hitting. That can however dull the needle, but you’re not supposed to reuse needles anyways. If you are eating out with family or friends, one of them can assist you to the restroom &/or inject you after a bit of training.