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Explanation
The comic shows two people in conversation. One says: "Roll a ball up a hill? Certainly! However, that'd require a reduction in entropy which clearly violates the second law of thermodynamics." The caption at the bottom delivers the punchline: "Creationist biologists aren't nearly as bad as creationist physicists."
The joke plays on the common creationist misunderstanding and misapplication of the second law of thermodynamics. Some creationists argue that evolution violates the second law because it produces increasingly complex organisms, which they equate to a decrease in entropy. This argument is flawed because the second law applies to closed systems, and Earth is not a closed system -- it receives energy from the sun, which allows local decreases in entropy.
The comic takes this flawed reasoning to an absurd extreme by imagining a "creationist physicist" who applies the same bad logic to everyday phenomena. By this reasoning, rolling a ball up a hill (which locally reduces gravitational potential energy entropy) would also be impossible, which is obviously ridiculous. The humor comes from demonstrating just how silly the creationist misuse of thermodynamics is: if you applied the same reasoning consistently, you would have to conclude that virtually all physical processes are impossible. The final caption suggests that while creationist biologists are bad enough with their misunderstanding of evolution, a creationist physicist applying the same faulty logic would be even more absurd, since they would deny things that anyone can directly observe happening.