Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

This comic features Batman and the Riddler in an unexpectedly emotional encounter. Batman reads a note from the Riddler and begins to say "That's not even a riddle. You aren't --" before stopping mid-sentence with "OH GOD. Oh, I'm sorry... I didn't..." The Riddler, visibly hurt, responds with "Yeah, you DIDN'T." The two stare at each other in uncomfortable silence.

The final panel, labeled "Earlier...," reveals that the Riddler had slipped Batman a note asking "Did you remember my birthday?" -- not a riddle at all, but a genuine, vulnerable personal question. The humor comes from recasting the adversarial Batman-Riddler relationship as something more like a neglected friendship. The Riddler's usual gimmick of leaving riddles is subverted; instead of a clever puzzle, he's making an earnest emotional plea. Batman's guilt and the Riddler's wounded reaction suggest a deeper, sadder dynamic beneath their comic-book rivalry, as if even supervillains just want to be remembered by the people in their lives.