Depends on the person and the activities. As mentioned before, allot of Scots go regimental which means no under wear, but there are those who feel under wear is a must. Just depends on the person, I was raised that under wear made you’re kilt a skirt, so I typically wear mine regimental. The only time that I wear under wear with mine is when there an obvious reason to, such as stadium seating venues and activities that may save my company any embarrassment from any voyeurs. Most of the time however, no undies.