I remember when I was 17 my parents were staying out overnight one Saturday evening and I was tasked to look after my younger sister. They had agreed she could have a friend stay over, and she and her friend Chloe disappeared into her room not long after my parents left. Later that evening I'd had a shower and was lounging around on the sofa in just a pair of loose shorts and a bath robe. I'd settled down to watch a late movie when my sister and Chloe barged in saying they wanted to watch too. My sister was wearing her usual girlie pyjamas but Chloe had just a nightshirt on which reached mid-thigh. I'd never taken much notice of Chloe being my sister's friend, but I was beginning to look at her in a different light. She had her blonde hair tied back in a pony tail, and her budding young breasts were poking through the thin material of her night-shirt. However it was her long, slim and tanned legs which attracted my attention.
They decided to crash out on some scatter cushions on the floor, and were laid down on their stomachs in front of the TV. The film began which was a horror type movie to which the girls were both giggling and screaming at. Chloe's constant wriggling around on the floor meant her nightshirt had crept up to just below her butt, and I was hoping for a glimpse of some panties. I wasn't disappointed when a little later her pale yellow panties came into view. They were creeping up her butt crack and that glorious v-shape of her panties between her legs was tight against her pussy. I could just make out the outline of her pussy lips as she continued to move around on the cushions. By now her nightshirt had ridden most of the way over her butt and her perfectly shaped butt cheeks stood out against the yellow panties.
My cock was now rock hard and I slunk down on the sofa and lifted my leg so they could not see what I was doing should they turn round towards me. I crept a hand inside my shorts and slowly stroked my cock whilst looking at Chloe's perfect butt. I didn't know if it was my imagination but Chloe seemed to rocking back and forth slightly, pulling those panties hard against her pussy. I continued stoking my cock beneath my shorts now totally focused on Chloe's butt. The edges of her panties seemed come together and I was sure I could now see part of her pussy lips. They seemed smooth and hairless as she carried on rocking to and fro. I could feel that tingling sensation at the base of my cock and I knew orgasm was not far off. Without her eyes leaving the TV, Chloe reached around to adjust her panties and pulled them out and to one side. I briefly had the greatest view of her smooth teenage pussy before being covered over. I could now see the damp patch on her yellow panties which had me pumping ropes of jism into my shorts. It felt like I was cumming for ages but was probably just a few seconds, the girls being totally oblivious to what was going on behind them.
The following morning they had both gone to the mall and I found those yellow panties in her bag. What I used them for is another story!