I have read a lot of the contributions on Solo Touch, and now, FINALLY, I have my own to add. This happened for the firt time last year, although there have been several repetitions.
I jack off regularly, at least once a day, sometimes more. Sometimes, though, although I have no trouble getting hard, I find it difficult to cum. At those times, I need to think about something more than just being with a girl or fucking. This particular day, I had the house to myself and was having trouble getting off. I walked around the house naked with my hard-on. It felt good, although even that wasn't enough. I tried jacking in several rooms, before ending up in my sister's bedroom. Allison is two years older than me and definately a looker.
I stood in her room rubbing myself wondering if she played with herself too. I pulled back the covers on her bed and found that the edge of her lower sheet was stained white, about half way down the bed. I wondered if she likes to straddle it and hump it. So I kneeled down and smelled it and OH yeah! definately pussy. It was then that I had the idea. I rummaged in her hamper and found her panties, stained white and still moist. I held them to my face and rubbed myself. I was almost dizzy with it all. I felt the orgasm boiling up inside me and then, BLAM four huge ropes of cum, I had cuaght it in her panties. As I subsided, I looked at my come covering Ally's. Then I just stuffed the panties back at the bottom of her hamper.
I have done this many times since.
I hope Allison never finds out though.