The answer: Nothing. All parts are in perfect working order. Seriously, though, people ask me this all the time.
For hundreds of years the standard was that men did not wear anything under a kilt. This strikes me as very impractical even at the best of times, not to mention drafty, but there it is. In more modern times, I have seen everything from “nothing at all” to polka dot boxers. Male dancers wear dance trunks, as do female dancers. I generally suggest some kind of lycra shorts (like Underarmor) for men. Women know what to do.
This has come up recently in Scotland in the kilt rental industry. Because of cleaning costs (?!) and sanitary concerns (???) all rental customers are asked to wear underclothes when they wear the rented kilt. One could argue that this goes against tradition, but in the interest of cleanliness I can understand it.
I really appreciate the comments that people leave. Yesterday’s comment is the reason for today’s post. If you have other questions or comments, please feel free to leave them. I will do my best to answer.