I'll recount two stories where this applies.
1) There was a girl in middle school (7-8) who was good looking, but compared to the other girls in the class, she was probably average or above average. I went to a private school so uniforms are mandatory. In the first year, all she wore was tight or biker shorts under her skirt. She was very oblivious when it comes to knowing that she was exposing what was underneath. Examples would be playing basketball and her skirt flies around and she sits with her ankle resting on her leg- not fully crossing her legs sometimes. In the beginning of the school year, she would hang out with girls that are physically active and hot. Later before school ended, she would hang out with another group of girls that were not very attractive or active. They would just sit and talk during break. Then during that time, she switched the shorts for panties under her skirt.
The beginning of next year: we were getting ready for class. She came to school and then bended down to tie her shoelaces. As she was tying them, I noticed that she was wearing white panties. I stood there shocked. She always wore shorts underneath last year, maybe she forgot to wear them today. The next day, she was wearing panties again. It was like that throughout the school year. She always wore three types of panties: white, white w/stripes, white w/dots. Unlike the other girls, she was very easy to look up
She would sometimes wear shorts under her skirt later in the school year, but she was clueless that you could still see her panties under since the shorts were a little baggy. During that year, she looked sexier than before because of that little change underneath her skirt.
2) I was working as a temp in office setting. All I did was work in front of the computer. There was a girl who would pick up a couple of documents from my room every day. She had red hair, wore loose fitting clothing, and not a lot of make-up. I didn't think much of it until one day she came with clothing that she doesn't usually wear.
I was sitting at my desk doing crappy work where she came in and said hi. I stared at her and it took like 5 sec to verify on what I was seeing. She was wearing tight fitting clothes. Her hair and make-up was done well. It seemed that her chest size grew from an A to a C overnight. I said, "you look different today." She said that she wore this because her friends were picking her up after work to go on a night out. She wore this every Friday. I worked with another guy in the room. Everytime she would bend down to pick up the documents, I could see down her shirt or blouse. She always would lean toward my direction. I don't know if she done this on purpose.