Hi, This just happened today!
During art class my friends and I got to chatting and for whatever reason one of the girls said she was feeling horny and told us that she had seen one of the girls, in the physical education class, when she was in the gym dropping off something to the teacher, sitting on the floor, and from where (camile, my friend) was standing, was able to see this girl was wearing nothing under her shorts and was even touching herself too.
Well, of course just hearing that set off a bullet and one by one each of us started blushing and told each other we were now horny.
After class ended, I raced to the changing room to change (had dance team practice during lunch).
I kept thinking about what Camile had told us in art and felt myself getting aroused by it. As I was changing, my hand brushed over my crotch on top of my undies and I felt such a tingle down there. I just wanted to do more then and there, but not being alone, I walked into the area where the toilets are and went into one of the two stalls. I sat down and started to rub my nipples and touch my clit and slide my fingers around a little. Then I heard soft moans, gasps and whispered words from the next stall.
I lowered my upper body onto my lap and looked under the stall wall and could make out that the girl in the next stall was in the midst of masturbating. Well, oh my, hearing her and touching myself made me wetter and I too began to furiously work on my pussy by jamming three fingers into me and I had an intense orgasm about the sametime that my unidentified neighbour in the next stall did. After I came, I sat there for a minute or two to calm down and seeing that I was there already, (blush) made use of the loo and then went to get ready for practice.
I never did see who it was, but it was fun to get off and listen to someone else doing so at the sametime not five feet away from me. Maybe next time I hear her we could have a mutual. If so, I will share it with you all.
Have a nice night!