algebra
Explanation
The Joke
A teacher or public figure announces that schools are "no longer teaching algebra or calculus because they're not useful in the real world." The audience cheers. The comic then cuts to "Later," where a child excitedly tells their parents "I shall become..." -- and we see they want to become The Riddler, Batman's villain known for obsessive puzzle-making. Batman is shown reacting with "DAMMIT!" The implication is that without rigorous math education, aspiring young minds channel their love of problem-solving into supervillainy rather than productive careers.
The secondary layer of the joke is the running cultural debate about whether advanced math courses are "useful in the real world." The comic slyly argues that math education does serve a purpose -- even if that purpose is keeping potential supervillains occupied with homework instead of crime.
The Humor
The humor works on multiple levels. First, there is the absurd logical leap from "we stopped teaching math" to "now kids are becoming supervillains," which is a classic SMBC exaggeration of a real-world argument. Second, there is the specific choice of The Riddler, whose entire identity revolves around puzzles and logic problems -- exactly the kind of thinking that algebra and calculus would satisfy. Batman's frustrated "DAMMIT!" sells the punchline by showing this is a foreseeable consequence that no one considered. The caption "How am I the only person who's considered this consequence?" (visible in the bonus panel area) adds the final layer of Weinersmith's signature self-aware humor.
References
The comic references the ongoing public debate about the relevance of higher mathematics in school curricula. The Riddler (Edward Nygma) is a DC Comics villain who challenges Batman with elaborate puzzles and riddles. This comic was also a promotional tie-in for Zach and Kelly Weinersmith's book "Soonish," as noted in the bonus text.