Found a lovely documentary discussing speedos, how they were created (featuring Peter Travis, the designer of the original Speedo), their connection with the gay men's community (at least in Australia) and a few words on fetishist who enjoy the swim brief. Short vid, 23+ minutes and NSFW for scenes where a tumescent penis may be viewed both in and out of togs.
https://www.youtube.com/watch?v=ye603by2HRM
enjoy!