First time I saw someone have an orgasm
This happened when I was in my teens. It was summertime, and my cousin Shannon (who is a year older than me) and I had been laying out in the sun in our bathing suits at my house. We had spent the time talking about boys, though neither of us had any experience. We spent probably two hours outside, then we headed back into my bedroom to get changed.
I had two beds in my bedroom because I often had sleepovers. Shannon and I were sitting on the beds, facing each other. I had noticed that her nipples were hard, because I could see them through her bikini top. She looked at me funny and simply said "I need to have a rub". I had no idea what she was talking about. I had never touched myself down there before.
Without even blinking she pulled her bikini to the side and started rubbing up and down her slit, then started rubbing in circles on what I later found was her clit. I didn't understand what she was doing, so I didn't touch myself.
Shannon then laid back with her legs still hanging over the side of the bed, and while she was rubbing her clit she pushed a finger deep into her pussy. Her fingernails were painted hot pink, and it was hot watching it disappear inside her.
She kept rubbing and rubbing, and her breathing got faster. Then suddenly she let out a low groan and that was it. She sighed, pulled her finger out and pulled her bikini back over her pussy. I just sat there looking at her with big eyes, and she laughed and went on like nothing had happened.