hmm
Explanation
The Joke
Batman tells Robin that they can't fight the Legion of Doom alone — Robin is not experienced enough, the odds are bad, and they need an army of Batmen. In the next panel ("Later"), we see Batman and Robin looking at a newspaper or comic book ad in the back of a magazine — the kind that used to advertise novelty items like X-ray glasses and sea monkeys. The ad reads "Another Boy Fancy With A Murdered Family" — a darkly hilarious classified-ad-style recruitment notice for more Batmen.
Robin has a confused reaction, as the plan has gone from "we need reinforcements" to "let's find more orphans whose parents were murdered."
The Humor
The joke works on multiple levels. First, it points out that Batman's origin story (parents murdered, child becomes vigilante) is so specific that "recruiting more Batmen" literally means finding more children who witnessed their parents' murder — which is horrifying when stated plainly. Second, the format of the recruitment ad (styled like a cheesy magazine classified) creates a tonal mismatch between the gravity of the premise and the casualness of the presentation.
The bottom panel promotes "Sawyer Lee and the Quest to Just Stay Home" — a book/project advertised alongside the comic, styled as a parody adventure story for people who avoid adventure.
Context
SMBC frequently deconstructs superhero tropes by following their premises to logical but uncomfortable conclusions. Batman's origin story is particularly ripe for this treatment because the "dead parents" motivation, when examined rationally, raises troubling questions about vigilante psychology.