I wear guy thongs. My favorite place to buy them is Flexables.com. They come in cotton or lycra and a multitude of colors. There are made to fit a man's shape.
Flexables are excellent; the microfiber is very comfortable and I have too many of them!
In nylon, Sundown is very good too but are much more structured.
i do thongs with microshorts, blokes thongs, but i do have to watch for fallout (not boasting, just the way they are). Either that or freestyle, which is most of the time...