This happened one hot, sleepy and dull afternoon in my secondary school here in the UK. It was many, many years ago now, but I often think of it to this day.
Chris sat to my right across a gap in the rows. We had THE most boring history teacher in the universe. History lessons for us were reading several chapters of a book and then answering multi-choice questions. NEVER any variation, always the same.
One afternoon, we had been set the nightmare of reading 6 chapters of the book. (I think the teacher wanted a sleep!) We all settled down in the airless classroom to get on with it.
I noticed Chris sneaking quick glances at my knees. Now, I never fancied Chris at all, and nothing other than this ever happened between us, but, well, I was bored, and I guess I may have been a little bit horny too.
I inched my skirt up to show him my knees and a little bit of thigh. Chris sighed and I saw his left leg appear from under his desk. Then I noticed to my utter amazement, the material of his trouser leg moving - rhythmically - he was rubbing himself!
I let him see a little more, up the inside of my left thigh (as he was looking at it.) Not up to panty level, but more than I had EVER shown a boy before, that's for sure!
He leaned back and I nearly fainted! He had his cock out. And I mean FULLY out, AND he was hard as a board. I could even see that the tip was wet with what I later found out was pre-cum.
I felt an immediate flooding between my legs as unashamedly, he masturbated looking at my legs.
I had my legs apart as far as my too-tight skirt would let me, and although he was getting a good look up my inner thigh, I knew he couldn't see my panties.
He wrote on his notepad. "I'm going to cum - wanna watch?" I nodded and then he said "I don't have anything to cum into."
I reached into my bag and grabbed the spare panties I always carried and passed them to him. Although they were clean, he still smelled at them before taking time to arrange them so that the crotch was to hand for when he came. Then, with my heart thudding and my mouth dry, I saw him unload into the very crotch of my panties.
I had never seen a boy cum before, I had never seen sperm, and I had never had a boy's sperm in my panties.
He balled them up and casually passed them back to me. I stuffed them in my bag and returned to my book.
At the end of the lesson, I made sure I was first out, and hurried to the bathroom. In there, I got my first look, smell, (OK, and taste) of a boy's cum.
Did I masturbate? HELL - you bet!
I understood totally, from that second onwards why boys are obsessed with the smell on a girl's panties. I knew I loved everything to do with sperm!
I wasn't on the pill then, but I do remember I desperately wanted to put those messy panties on - so I could say I had a boys cum against my pussy, but I was too scared of getting pregnant. Of course, I know now that the risk would have been remote, but not impossible, so I did the next best thing - I wore them OVER my existing panties.
Of course when I got home I had a problem I dare'nt let my mum find sperm in my panties, so I washed them through and dried them myself.
That was the only time I did anything with Chris. I don't know that I wanted more, but doing that in class was just SO erotic.