I'm inclined to agree with OP. The other customer might at least have asked if being around needles or injections caused him to have an adverse reaction like fainting or vomiting or left him feeling uncomfortable. I see the dining companion as selfish and inconsiderate.
I disagree with @Leper. Injecting in public is nothing at all like breastfeeding. Injecting in public uses a potentially dangerous implement, a needle, which can cause stab injuries; after use, a needle is even more dangerous as it may now be a source of blood-borne pathogens.
Taking blood readings in public is also inconsiderate and selfish in my view and may cause discomfort or create dangers for others. This procedure also uses a a needle (or lancet) to create a wound to produce blood (a droplet), the blood is transferred to a test-strip, which is then inserted into a machine which does the reading.
At the end of the procedure, the following items are potential infection sources:
- The lancet
- The test strip
- The test machine
- The tissue or hanky used to clean blood from the puncture wound.
If I need to do this testing away from home, I do so in a stall in a public toilet, flushing tissue away. I carry a secure, hard-plastic container (an old test-strip dispenser) for the used lancet and test strip in the wallet for my test-kit. And needless to say, I wash my hands before and after testing.
I have of course being diagnosed as diabetic several years ago.