Gosh, I love reposting things that are under Creative Commons license.
Like pretty much all xkcd strips, it's awesomely, geektastically funny. But I'd like to draw your attention to the little visual aid in panel two which reads 'Standard Creepiness Rule: Don't date under (age/2 + 7)'.
This rule explains rather a lot about Batman/Robin and Superman/Robin pairings ...if you take into account the way many people have trouble remembering mathematical formulae correctly. (Don't believe me? What's the formula for the circumference of a circle?1 How about for the area of a right triangle?2) Here's what I think happened.
In Bruce's head, it's 'Don't date under (age/7 + 2)'; so, if he's 35 -- and canonically, he's always 35 except when otherwise specified such as in Batman: Year One or 'The Lesson' -- this yields a don't-date-under age of seven years old. Perfect for Bruce, who in ever so many ways is still an eight-year-old boy in a man's body.
In Clark's head, the Standard Creepiness Rule is 'Don't date under (age/2 - 7)'; so, if his default canon age is 30 -- which, officially, it's either 29 or 30, but I don't want to clutter up this post with tedious remainders -- this yields a don't-date-under age of eight. Perfect for ...Clark's tendency to fixate on Robins from the moment he first lays eyes on them in uniform. Especially when one takes into consideration that, while modern canon has adjusted Dick Grayson's age at the time of his parents' death to thirteen, in the Golden Age Dick went to live with Bruce and fight crime in short pants before he was even ten years old (the number of birthday candles on the cake in this issue was frighteningly small, but unfortunately the internets failed to provide me with any scans showing the post-spanking panels).
See? It ALL MAKES SENSE NOW.
1. Hint: *not* πr2.
2. Hint: *not* A2+B2=C2.
ETA: Cross-posted to my my InsaneJournal here. Comments are enabled there. I sincerely apologise to anyone who finds IJ's theme offensive; I weighed this concern carefully against the need to have a journal host I felt I could trust not to arbitrarily delete my content. I hope to find a compromise which is more accomodating of both issues soon.