Society as a whole doesn’t generally accept the idea of men wearing things like thongs or bikini style bathing suits. The most common reaction is that men don’t look good in them. I contest that. I don’t think that’s what’s really going on.
I think it has more to do with two things:
1. People just aren’t used to it.
If you don’t see something enough it looks odd and out of place to you. You already hav a preconceived notion of what men and women should wear. So when someone breaks that concept, you will either laugh or be shocked into disgust. But if it becomes a regular thing, eventually it’s no big deal anymore. You may still have an opinion.
2. Men are hairy.
But so are a lot of women naturally speaking and they shave their legs and their bikini areas to look better. So if men did as well, it wouldn’t look as bad. Because anytime you have tigher clothing, hair just doesn’t go with it. either for women or for men.
You also have to take the guy in context. Obviously you can put a old fat hairy man in a thong or bikini bottom and conclude that “guys don’t look good in those.” But neither do old fat hairy women. Put a nice skinny/toned younger shaved guy in one and now you have something to compare.