If you read the quote you quoted, he said “usually pretty easy” not “always absolutely certain.” So usually it’s pretty easy to identify primary and secondary sexual characteristics, especially with a naked person, as to who is male or who is female. This method is not foolproof. Good on you for pointing that out.
Roddy
It would really freak me out knowing there is gay guy looking at me in a sexual way or having sexual thoughts about me.
How does someone look at you “in a sexual way”?
I don’t know anything about you, but to be honest most guys I’ve heard say that weren’t the sort that would attract that attention anyway.
If you are the sort that would, odds are very high that’s happened before and will happen again.
Oh, you know. In the way that I’m looking at sweat209 right now.
How you doin’? 
For better or worse…
In reading along with this thread, I’m reminded of a skit on Chappelle’s Show. The premise is why you couldn’t do the inverse of the Mel Gibson movie “What Women Want,” where he is able to hear the thoughts of women. If you had a movie called “What Men Want,” where a woman had that ability…
Scene: Elevator. 5 or 6 men in business suits. One kid. A woman enters the elevator.
Voiceover:
(Man 1) “Man, if I could just slide a finger down the crack of dat ass.”
(Man 2) “I wanna have doggy style sex with her.”
(Man 3) “Damn, baby, check the nipples, man.”
(Kid) “I’d put a hurtin’ on that bitch…daaaaaaaaaaaamn.”
Now, before anyone white knights and objects that “I would never objectify a woman that way,” the skit is obviously satire and doesn’t speak for all men, but there is certainly a subset that it fits exactly.
Point is, the audience laughs because either they know “that guy” or they are “that guy.”
No doubt many women on the board could chime in and say that there have been times in their lives where they’ve felt the ogling of men. Maybe it makes them uncomfortable, or maybe they’re flattered, or maybe they don’t care either way. But the cultural attitude seems to be “hey, you’re a pretty woman, you’re going to get ogled.”
This whole locker room thing just turns it around and brings out that, hey, there are some men who’d feel uncomfortable being ogled by another man. But the reality is–just as women will be objectified–so will men, often by other men.
What I don’t think many people consider (or perhaps even know) is that, while the self-reported incidence of homosexuality is a relatively low percentage of the population as a whole, the spectrum of sexuality is actually pretty wide, with a fairly low self-reported incidence of exclusive heterosexuality. Most people find themselves somewhere in the middle.
As an example, go to your city’s Craigslist site. Open the “Casual Encounters” link under “Personals,” then select the “M4M” option. Notice how many “straight” or “bi-curious” men are looking for a male encounter. Truckers on long-haul, closeted or curious married men with families, etc. Gyms are especially popular, and I can personally attest to being ‘hit on’ quite a few times in the hot tub of my fitness center–probably by men who’d self-identify as “straight.”
There are, very likely, a lot more men around us every day who check us out, and a certain subset of them probably have an internal monologue similar to the skit above. Should that make us scared?
At the end of the day, even though I’m pretty far towards the hetero end of the spectrum, I’ve always been flattered when anyone found me attractive. If a dude sneaks a peek at me in the gym shower, what harm is done? It doesn’t make me question my own sexuality, so…what’s the big fuss?
I like your post. I also LOVED Chappelle’s Show, (though I really understand why Chappelle might have thought that some people might have been laughing at the wrong things - but that’s off topic). I know the skit you’re talking about. Hilarious.
I didn’t know it bothered you that much; guess I’ll have to stop. Maybe.
Oh, and have you ever looked at a woman “in a sexual way”?
The system we have now is fine. It works, and no one is really bothered by it. Your friends, dedicated gym rats that I’m sure they are, have almost certainly shared a locker room with a gay man. They have emerged from the experience unscathed. The Michael Sam issue is between him and whatever team drafts him. I’m sure that team will figure out a strategy to cope with the drama.
I wanted to give Larry Borgia the last word, but I just wanted to thank everyone for contributing. Like I said; I understand why some people might be mad at me, or upset with me. I bet it would be upsetting for me if I were gay or bi to read some of the things I’ve said. I sent one of my friends the link to this thread, (I would send it to all of my friends, if I didn’t have such personal stuff written here on Straight Dope in other threads).