When I was a junior in high school, I spent the evening at my (female) friend's house and we ended up talking about masturbation. Although I had learned to masturbate a couple of years earlier, my friend had never touched herself before and had never had an orgasm. I was too shy to pull down my pants and show her, so I explained how 'other girls' did it and she said she would try in the shower the next morning.
When I saw her at school that morning she was SO excited-she said she had made herself come TWICE in the shower that morning and told me how great it made her feel. Then she said that from now on, she was going to masturbate every time she took a shower (which was about the only place she had any privacy at home).
Although I'm not particularly attracted to other girls, the mental image of my friend rubbing herself in the shower kept popping into my head for the rest of the day. The more I thought about my (somewhat goody-two-shoes) friend getting herself off, the more excited I got, and by the time I got home, I was ready to do some serious masturbating myself.
My friend and I both took our showers at about the same time every morning, so when I stepped in the shower the next morning, I started thinking about what my friend was probably doing at that very moment just a few blocks away, and pretty soon I was grinding my pussy against a big bar of soap. When I finally came, it was one of the strongest orgasms I've ever had.
I wasn't sure if I should tell my friend about it, but when she told me 'I did it again in the shower this morning', I (unintentionally?) blurted out that I had too. She giggled and told me that she wondered how many other girls did it before coming to school.
Since that day I've masturbated almost every time I've taken a shower and even though I have plenty of privacy now, the shower is now my favorite place to touch myself.