This happened when I was 16 and it actually happened in a school toilet, although it had started in a classroom. At the time, I was really disgusted with myself, but lately, it's all I masturbate over.
Her name was Rachael, and oh BOY did she think she was something special. Her family were easily the wealthiest in the neighborhood, and she was always beautifully dressed. She had a little group of hangers-on, not friends, just people who were as shallow as whe was and who wanted to be seen with her. Think Sharpay, High School Musical and you get somewhere close. (Although Sharpay was nicer!)
Rachael would usually talk to me, pretty much every time it was sarcasm, but sometimes she would talk as if she actually liked me.
So, one day, to my utter amazement she plonked herself down next to me at the desk (the older, two-seater variety) at the back right hand corner of the classroom. I was right in the corner, she was next to me. Her expensive perfume drifted lazilly on the summer breeze. The lesson, of course, was dull beyond words. There is only so much you can do with irregular French verbs!
Rachael was not paying the slightest attention. She was leaning on her elbow and just looking at me as I tried to concentrate. Then, without a word of warning, I felt her hand on my leg and moving North! She didn't stop, she didn't ask, she didn't hesitate. I knew she was going for my crotch but to my surprise, I found myself parting my legs to let her. She moved disdainfully up unto she was brushing my rapidly dampening panties with her finger. She let me get good and wet and then took her hand away. Then, still staring at me, she smelled her finger and her lips curled. 'Yuck!' she whispered. I was bright red partly with embarrassment and partly with being horny. Then she whispered. 'Let's get out of here' before raising her hand and calling out (again, to embarrass me) 'Miss, Anna has come on. Can I take her to the toilet?' The teacher, a man blushed up and said 'Uh.. yes, of course.' The whole class, boys AND girls stared at me as we left the room.
Of course, it was nowhere NEAR my time of the month and it was typical of Rachael to say something like that. She took my arm and guided me to the girls bathroom. Once in there she draped her arms around my neck and looked me in the eyes. 'Anna, your cunt stinks. I am doing you a favour by doing this.' She dropped to her knees and tugged my panties down before uh... kissing me there and pushing a finger up me. We were right there, in the communal area of the bathroom where anyone who walked in would see me. Anna fingered me and licked at my clit until I felt an orgasm building. Suddenly, for the first (and only) time in my life I was cumming at the touch of another girl. And cumming harder than I have ever done before OR since.
Anna looked up and said 'There, you dirty little bitch. Now do me.' I had never even THOUGHT about touching another girl, let alone using my mouth as part of the deal, but I knelt as ordered and leaned in to kiss her there, but she said 'Ugh.. no, I don't want your mouth on my pretty little pussy.' So I fingered her until she said 'Take my panties off. I don't want them to smell like yours.' I slid them off wondering what was so wrong with that special female scent. But I might have guessed Rachael knew what was coming better than me.
So I fingered her harder and harder as she asked me until she said 'Ohh.. I'm cumming.' Yeah,, she came... AND squirted a HUGE amount all over my face, and my school shirt. After she smiled.. 'Sorry. I always do that when I cum. Bye.' and so saying she walked out, leaving me kneeling there soaked through. It smelled musky, but I was pretty sure there was pee too.
I ran home and threw all my clothes in the washer. At the time I was disgusted, but lately, I make myself cum all the time thinking about Anna.