Umm, some mystery: We already know that Smithers is gay and has erotic fantasies about Mr. Burns. One episode even showed him learing at a nude images of Mr. Burns. The question is who ELSE on the Simpsons is gay. I'm pretty sure they've suggested Sideshow Bob is gay, haven't they?
Patty Bouvier is not gay; we have seen her lust after men before; given the number of occasions, saying she "rarely" dates men is odd.
Comic book dude gets excited about female comic-book characters, but that could just be because they're so cool. Ya know, the way drama queen queens get worked up over Barbara Streisand. So he could be gay.
I've never been to sure about Mel... could be bi. But he's in ads going after Marge. Barney could also be bi for all we know. Neither seem gay, but both could be used for that, "you never know who" sorta twist.
I also wouldn't be surprised if the Kennedy-esque mayor was used to satirize Governor McGreavey.
I'll bet it's Apu (pu).
I can't believe I just caleld Moe, "Mel."
Possibly. "The Simpsons" is not known for continuity but: Comic Book Guy had a fling with Skinner's mom, and also said (after receiving Homer's "Mr. X" email): "Do I dare cross the final frontier?"