I know what you mean. I went to a very preppy private school with a dress code similar to what you described for the boys and nice pants or skirts and blouses with collars for the girls. In the late 1980's I arrived at a big state school where everyone dressed in whatever they wanted including the professors. I experienced a sort of culture shock. Next thing I know out comes the acid wash.
Unfortunately some people didn't know how to dress when the occassion called for it. For example in 1989 or 1990 there was a regional NPC meeting at a college one hour away so all of the sororities from my school were going. My sisters and I decided to wear dresses or business suits and our sister pins. The embarrassing thing was one sorority from my school showed up wearing sweatshirts with letters and jeans and their pins. The reps from their sorority told them that they weren't dressed appropriately for their pins or the occassion and gave them a hard time. We knew a lot of them since we went to school together, and they didn't understand what they had done wrong. We didn't understand how they could be so clueless. It was pretty bad.