thermodynamics
Explanation
The Joke
A man confidently declares that "evolution is impossible" because "the 2nd law of thermodynamics says chaos always increases over time," and therefore you cannot go from rocks to conscious beings. A woman suggests he consider "getting a more ordered conception of physics," to which he responds indignantly: "I just told you it's impossible!"
The Humor
The comic targets one of the most common and persistent misconceptions used in creationist arguments against evolution. The claim that evolution violates the second law of thermodynamics is a classic misunderstanding: the second law states that entropy increases in a closed system, but the Earth is not a closed system -- it receives enormous energy input from the Sun, which allows local decreases in entropy (like the development of complex life) while total entropy in the broader system still increases. The man in the comic not only misunderstands the physics he is citing but is so committed to his conclusion that he cannot even process the suggestion to reconsider. The woman's response is a beautiful double entendre: she is both suggesting he learn more physics and noting that his own thinking is quite disordered.
References
The second law of thermodynamics, formulated in the 19th century by Rudolf Clausius and others, states that the total entropy of an isolated system tends to increase over time. The misapplication of this law to argue against evolution has been a staple of creationist literature for decades and is widely debunked by physicists and biologists alike.