Boy, before my knee surgery, I sure hope no one was judging me when I parked in a handicap spot and walked into a store. Because I had rested my leg while driving, I could usually walk freely for the first few yards. Gradually, though, the arthritis pain would come on, so that, leaning on the grocery cart, I would often have to judge whether I could walk to another part of the store, bring the car around, or just skip getting what I wanted. By the time I headed out of the store, I would be sooooo glad my car was close by.
Another thing about arthritis that make it hard to tell by looking at another person is that the pain comes and goes, perhaps minute by minute, sometimes hour by hour. And some days are better than others. Nor does a person have to be limping to be stiff or in pain.