let's go back a little, this is not me now, this is me about 22-23 years ago. I don't need to tell you how men were socialized to be freaked out about homosexuality. I lived in South Beach in the 90s and I don't think I have to state what the scene was like. Even then, at 22, I was never bothered about being propositioned or hit on, I thought it was a compliment that another human being thought I was interesting in some way. However, being naked in the shower with this friend and subsequently realizing that I was the object of his sexual desire was a totally different thing than being at a bar or walking by the street and being stared at or being propositioned. I think it was deceptive on his part and my reaction was very mild.
Now, if I had known he was gay (once he came out to me there was no more bi, girls went out the window) and had no clue he was interested in me, I have to say that at the time I would have thought twice about hitting the showers with him. It was not a fear that I would want to jump him, I did not*, but I would have felt insecure about potentially being the object of his desire in that setting**. Again, fully clothed at a restaurant, bar, whatever, no problem. Why the insecurity? Crap, it is/was not the norm, kids today and younger guys may be very cool with it, but that is not the environment in which I grew up in the 1980s. Nobody my age grew up thinking that the guy fixing their car, etc. etc. may want to fuck them, your analogy in the setting of men and women is not accurate.
So, let's explore more, what is your theory? I knew I would open up a can of worms

Interesting that a woman can have threesomes, be with another woman and all is well, at least in our little world, but men can't wrap their heads about doing the same. Again, it is deeply iinstilled in us from a very early age in many different ways.
* Would not have been my type anyway. Shit yes, we guys know when another guy is good looking even if we don't want to hump them!
** Today, I would not give a rat's ass, if a guy wants to stare at me in the showers and fantasize, well, go for it, so long as you don't touch me. Of course, this scenario is much less likely, I am not the guy I was 23 years ago, but then again, while physically it may not be a good thing, I like the older version of Pangloss much better