OK, hot weather riding is hot. Just like cold weather riding is cold. The solution, in either case, is the same: Use the right gear in the right way as required.
When it's really hot wearing less clothes/exposing more skin is NOT, repeat, NOT necessary OR effective. Even in the 80's or low 90's, it is still NOT necessary to ride without gear.
Check this article (echoes a great article that MCN did a couple years ago) for a solid understanding of how to ride in the heat safely and more comfortably:
Motorcycle Tips: Hot Weather Riding
I recommend that everyone read the ENTIRE article, but if you don't, at least read below.
Critical Excerpt:
"You may think your body is hot at 99 F, but it’s "cold" compared to air at 118 F. If you expose your skin to air that’s hotter than you are, your body just soaks up more heat.
The lesson here is that if air temperature is in the 80s or 90s, it helps to open up the jacket vents, or wear a mesh jacket. But once air temperature climbs above 99 F, the best way to keep from getting cooked is to keep your insulation on, and the vents closed. Desert nomads wear long, loose wool garments, both to keep the sweating skin in the shade, and to insulate the body from the hot air."