I have a medical condition which is that my thyroid doesn't work and doesn't make enough of the hormone it's supposed to. When it gets out of hand the base of my neck swells up, thankfully this isn't often but when it has happened people can be really mean. Also even when it's normal and people find out, say on trips where I have to write down all medical stuff on a form and I often get "oh, I thought only OLD people got that how come you got it", that really bugs me.
I just ignore them now, afterall it was only because of a bully that it was found out, by taking the mickey of my swollen neck and if it'd been left I might not be here due to the fact that my thyroid had wrapped itself around the main artery to my brain.
I also have huge scars on my knees and I do get funny questions about them, but never mind.