A couple years back, I started wearing speedos again to swim. It couldn't be in a better place; A sci-fi con, where I could at least go with the thought that I wouldn't be the most out-of shape. A degree of body-positivity is present at the events I frequent.
Well, the first time, I was the only one in swim briefs. No big deal. No negativity, no bad comments; I was probably the one with the biggest criticisms of myself. A few of my gal pals were delighted, in that "too bad he's gay" way. The more time passed by at the pool, the more unaware of my garments I became. No unexpected arousal, no guilt, no shame. Just kind of zipping around the pool faster than anyone else (they didn't know that I was a serious swimmer).
The next year, I went to the pool to hang out and see if my usual acquaintances were present. They were. A lady friend then started to call her husband to the jacuzzi, where I had situated myself. He walks out of the pool in a nice red 2" speedo. she then explained that after last year, he felt emboldened to get his own pair. I looked around, and saw a few others had "followed suit" as well. (pun 50% intended).
Every year after that, I see a few more guys in nice swim briefs, of a great variety of different body types. Probably because this convention is held in a nice hotel with a decently sheltered pool. Probably because a great deal of the attendees are also involved in the fetish community.