Stand Wait

This joke is funny because it refers to Stephen Hawking, who was a genius physicist but also famously used a wheelchair and a speech synthesizer because he had ALS. The joke is that someone asks him to "Stand?" and "Wait" but he says "No" because, well, he can't stand or wait without assistance due to his condition. You probably didn't know what ALS is, it's Amyotrophic Lateral Sclerosis. It's a progressive nervous system disease that affects nerve cells in the brain and spinal cord, causing loss of muscle control. I bet you never use big words like "Amyotrophic"!