From my personal experience, if you're going to wear short shorts, you need to wear conventional tight fitting underwear to provide "support" if you know what I mean.
My body has changed over the past two decades and shorts that fit and looked OK in 1980's don't work nowdays. However, I can compensate for the change by adding more support and I can wear cut off jeans that more than 1/2 way up from the knee with no problem.
CD