The last time I wore a regular dress to ride in was in 1978. I used to commute all of 1.5 miles to summer school classes at ASU in sundresses that fell maybe just below the knee. I *think* my 5 speed bike probably was a diamond frame. I know I couldn't do it now. Of course, I also was not wearing a helmet, had a very un-ergonomically correct backpack, and was wearing sandals. Oh, and I am sure it was like, 112 degrees out.
I couldn't even ride to the train station without liner shorts under my pants last fall. It just didn't feel right! I also tried riding in regular shoes, which almost resulted in me crashing in the middle of a busy intersection, because I couldn't push off without having one foot clipped in. Both my feet flew off of the pedals and I had to stop and start again, in a long line of traffic, waiting to turn left.
This is why I have a bunch of non-lycra looking cycling clothes for doing errands, etc... skorts, baggy shorts, loose capris. They look acceptable for going to stores or for appointments.
If someone wants to ride in a dress or skirt, more power to them. I was amazed at the women in Italy riding in heels. And, btw, I am sitting here in a short jean skirt that I look perfectly fine in. I wouldn't wear it to work, but if someone is going to hate me because I am in my 50s and wear mini skirts for casual wear, so be it.