Why do you think it's ok to make fun of people's disabilities in front of their face?

For context, this is a place I go to and this is one of the volunteers at the place. They know me and I know them but they don't know about my condition. Admittedly I have a twitchy hand sometimes and they made a joke about Parkinson's and how I'm gonna be like Michael J Fox. I'm actually gonna have a Parkinson's disease down the line but not right now. <br><br>What is wrong with these kinds of people? Why do you think it's ok to make fun of people's disabilities?