I've heard lots of "cheeky" responses, but I'm not comfortable with responding with just that, myself.

I don't use mine often, but I too "look good" and I am waiting for someone to say something one day.

I thought I would just respond that "I have Multiple Sclerosis, and am easily worn out by walking". I'll probably have to throw in something like, "These passes aren't issued without medical proof of disability, don't worry" too though.

Cherie