I've been told that I'm too young to need a disabled parking space. I have ME and fibromyalgia, and (depending on how that day's going) I use either one stick, two sticks, a wheelchair or - on a good day - I can manage by myself. Usually in a supermarket, I'll use the trolley to lean on so I don't tend to take my sticks with me (I can generally manage from the car to where the trolleys are kept).
I've also been told that I can't have ME because I'm out and about. At this point, I haven't been out of the house since Tuesday lunchtime (it's now Thursday evening) because the pain (a) makes it too hard to get dressed and (b) makes me slower and so I have difficulty crossing the road between my house and the rest of the village. Fortunately, when I'm like this, my DF goes and does all the chores.
I do get that it's difficult for people to equate (relatively) young - I'm 34 - and healthy-looking with disabled, especially when I'm dressed smartly. Sometimes, however, the reason I've dressed smartly, done my hair and put some makeup on is because without it I look like death warmed up and I need to boost my self-esteem enough to be able to go out. And a lot of the time, there's a HUGE difference in how I'm walking and how I look when I get out of the car on arrival to how I look getting back to the car having done whatever.