I can't wear a face mask and am exempt due to having issues which make it extremely uncomfortable and difficult to wear. At the start of the pandemic I used to explain to people who asked why I can't, but I was getting some nasty comments and it's made me quite cynical. When someone asks now, I just tell them to mind their own business.
AIBU? I think that rather abrupt response probably would sound unreasonable from the perspective of someone who has just asked a single question, but I have been getting questioned (feels more like an interrogation sometimes) for nearly a year and I am just sick of it.