OR,

If it's warm enough, why not:

Swim - Speedo
Bike - Speedo
Run - Speedo ?

When I did a "tin-man" (now "Olympic" distance) tri 20 years ago, this is what I wore. The speedo dried on the bike and was fine for the run. I have a bit of a belly now, so out of the water I will be sure to have on a shirt or singlet just so the dogs, horses, women and children don't spook. That was the uniform of the elite guys that day, also. Butt might be a little saddle sore the next day, but 24 miles of riding shouldn't do lasting damage.

Tyson