My roomie pointed me to a post by Sean Carroll on the recent incident involving Kos and a certain TBS web-ad for the show "The Real Gilligan's Island", featuring Mary Ann and Ginger in a pie fight.

I'll get the obvious stuff out of the way: Kos is a moron. His response was ridiculous, regardless of your opinion of the ad. It showed a complete lack of respect for his comrades and their concerns. He deserves to have his face buried in shit for a while. Fortunately the fallout hasn't been all bad: check out the resulting Women Kossacks bleg (warning: it's still horribly ugly in appearance).
As to the ad itself: I'll admit, I find it titillating. I clicked on it. I'm not particularly embarassed about that fact. But note this aside by Sean Carroll:

One indication of the fact that the world has not achieved perfect gender equity is the paucity of ads featuring oil-wrestling matches between hunky men in Speedos. Not, I expect, that such imagery would be very attractive to many people of either sex.

So, why is it sexist to watch two statuesque women smearing pie over each other? Obviously there's a certain amount of objectification inherent in making something arousing. But I don't think anyone in particular would complain, if it weren't that men didn't resolutely refuse to be made into sexual objects.

I shan't minimize the role of gender disparity in perpetuating this situation. For many (if not most) men, interactions with women continue to be defined by sexuality, and women are made to assume the role of sex object whether they want to or not. The same is decidedly not true of men; women are not given much freedom to express any notion of a male sexual aesthetic or to shamelessly objectify men (whether they want to or not). As many important people have said, and with more erudition and footnotes than I can manage.

But I don't think this is all. Not long in the past, there definitely was a notion of male physical beauty, one appreciated and even held forward by men. If we dip back into ancient Greece, male sexuality was prized even above that of women. E.g. Plato's Symposium, where this brief excerpt is just one of many lines celebrating the homosexual relationship above the heterosexual:

And am I not right in asserting that there are two goddesses? The elder one, having no mother, who is called the heavenly Aphrodite-she is the daughter of Uranus; the younger, who is the daughter of Zeus and Dione-her we call common... The Love who is the offspring of the common Aphrodite is essentially common, and has no discrimination, being such as the meaner sort of men feel, and is apt to be of women as well as of youths, and is of the body rather than of the soul-the most foolish beings are the objects of this love which desires only to gain an end, but never thinks of accomplishing the end nobly, and therefore does good and evil quite indiscriminately. The goddess who is his mother is far younger than the other, and she was born of the union of the male and female, and partakes of both.

But the offspring of the heavenly Aphrodite is derived from a mother in whose birth the female has no part - she is from the male only; this is that love which is of youths, and the goddess being older, there is nothing of wantonness in her. Those who are inspired by this love turn to the male, and delight in him who is the more valiant and intelligent nature...

This was unquestionably not a society with gender equity, but the sexuality of men was certainly celebrated.

So I think there's as much or more a component of homophobia inherent in the dearth of male sexual objectification. Men might be willing to accept such a position (or rather, to impose it on each other), except for their galloping fear of being perceived as bent. Of TV in Ancient Greece, women might have complained that it was sexist to show the Skipper and Gilligan mud-wrestling and completely elide the unworthy females (and what about Mrs. Howell?). In other words, there's nothing inherently sexist about two women having a half-naked pie fight. It's the underlying implication: who gets to decide what's sexy and what's not.