During one scene, the beautiful (but psychopathic) Mavis approaches Matt's man-cave. Through the window of the garage, you see a warm but dangerous glow of fire and Matt's hunched figure over it. (Matt has a bad leg from a brutal beating in high school, and relies on a crutch.)
"Hephaestus," I said.
"And Aphrodite," Nicola said.
We paused the movie and searched on the Internet. "diablo cody greek myth" and "diablo cody hephaestus" and so on. The closest we find is a GQ interview with Patton Oswald in which he refers to Charlize Theron as Aphrodite.
Of course, Greek is not quite the right mythology, and Hephaestus is not quite the right guy. Juno was the Roman version of Hera. The town in which Young Adult is set is Mercury, Minnesota--Mercury being the Romanized Hermes. And so Hephaestus becomes Vulcan and Aphrodite becomes Venus.
Diablo Cody clearly has a thing for Roman mythology, but we couldn't quite tell if it went much deeper than names and basic character traits. Venus was beautiful, but (like Mavis) she was also a psychopath (if such a term can be applied to a goddess).
What is truly baffling is that no one has, that we can find, written about this on the Internet. I'm posting this to be sure that at least one person has.