Quote Originally Posted by Dianyla
Just move quickly.

Or, a more practical solution is to pull a skirt on over the shorts, then pull the shorts down under the skirt. You can also use a towel wrapped around you as a coverup skirt to accomplish this - that's an old swimteam trick.
I've even seen guys using this trick - with a utili-kilt or even with a special "racing skirt" - yeah the thing had a lable on it that said that, but a nice big towel is the cheapest method. In any case I don't think for the most part that anyone is specifically looking - even guys can be respectful of other persons modesty when they want to be.
Staying in your sweaty shorts is not only uncomfortable, but tempting undercarriage problems too, so its a good idea to change out after a race.