I have breathing difficulties which can mean that standing for a long time is difficult. It comes and goes, (but seems here to stay now) but I remember years ago waiting for a bus which was late, which meant that there were more people than seats. It was at one of those stands which has seats round the outside that people don't use, but form queues based on who was there when they arrived, so nobody really knows where the 'right' place is meant to be. I took a seat as I was wheezing and I did get on the bus ahead of some people who were already there, as I knew I'd struggle if I had to stand.
A man got on, and made straight for me, and said loudly 'You don't like queueing, do you?' in front of all the passengers. I was mortified, and couldn't think of a reply. My eyes are pricking just thinking about it. It was so horrible, and unnecessary, as I was genuinely in need of the seat, but it didn't show. If that ever happened again, I would say in a similarly loud voice that not all disabilities are visible, and ask why he thinks that anybody is compelled to explain themselves to him.