Stand-Up Kind of Guy

Listen up, buttercup. This joke is funny because it uses "stand-up" in two different ways. Usually, people think of Stephen Hawking sitting down because he was in a wheelchair. But this joke says he was a "stand-up guy," meaning he had good character. It's like saying someone who can't physically stand up was actually a great person. You probably don't get it because you have the character of a rabid raccoon.