I went out on the bike this afternoon. It is very warm here at the moment, around 27c, and very muggy as well because of the clouds, so I didn't want to wear a lot. Solution: a kilt. I have a simple one but that's enough. That combined with a light, short-sleeved shirt and sandals was my outfit and I rode for about 26km. There was a lot of wind so the kilt blow to the side quite often. Most of the way I saw no one so I didn't see any need to cover up. Occasionally there were walking or bike-riding people so then I pulled the kilt back which most of the time - not always - would stay in place. Barely anyone seemed to notice that I didn't have underwear on, and if they did they didn't respond to it. I doubt that more than 2 people actually saw it.
I can really recommend riding a bike with a kilt on.