I had this many times too. Ex friend's husband spiked me once to show everyone how clever he was, figuring it all out that my illness was a ruse or charade etc etc. Thankfully I stank out their bathroom and have never spoke to them since. Husband fessed to a mutual contact who was so appalled, I was told. I don't miss them.

When questioned now I say something like "would you make people with Crohn's disease ill to prove your petty point?" My solution is to be very direct, because I am pushing fifty and have no time to deal with fear of being perceived or bad opinions. It is ableism plain and simple. Usually people who question me in my country are just idiotic and back off quickly. But awareness can be pitiful.