pale-blue-dot
Explanation
The Joke
A person returns from space travel and, echoing Carl Sagan's famous "Pale Blue Dot" speech, says something like "It's wonderful -- you've seen Earth from space! It's so small... so fragile." They remark on how miraculous and precious the planet is. But then their friends start asking them to bring back their sense of cosmic wonder to everyday life -- to bring their "share of the grandeur" into doing practical things. The returning astronaut flatly refuses, saying "I'm not gonna do that."
The comic contrasts the lofty, transcendent experience of seeing Earth from space with the mundane reality of everyday life. The astronaut had a profound cosmic perspective shift, but when asked to translate that into actual behavioral change or helpfulness back on Earth, they want no part of it.
The Humor
The joke skewers the gap between inspirational rhetoric and actual follow-through. The "Pale Blue Dot" perspective -- that seeing Earth's smallness should make us more compassionate and cooperative -- is one of the most beloved sentiments in popular science. But the comic suggests that even people who have had the most perspective-altering experiences will still revert to being unhelpful and self-centered when they come back down to ground level. It is a cynical but funny observation about human nature: cosmic awe does not actually make people better roommates or citizens.
References
The "Pale Blue Dot" is a famous photograph of Earth taken by the Voyager 1 space probe in 1990, and the name of Carl Sagan's 1994 book inspired by it. Sagan's accompanying speech about the fragility and insignificance of Earth in the vastness of space is one of the most quoted passages in popular science.