This was when I was in high school (15 years ago)
I would visit my friend's house daily and would hang out there till night-time. He had an older brother and sister. His brother had already moved out, but his sister still lived there. She was fine. Very petite and demure. Sometimes my friend would take off and leave me there for a while on my own. We grew up together so he trusted me.
I was hanging out in his room and went to take a piss in the bathroom. I noticed a pair of her panties hanging out from the hamper. I can still see them to this day. Red, and silky, but more important, used. I picked them up and put them to my nose. The aroma was so powerful that my heart started pounding and got extremely horny. I couldn't help myself. I started jacking off right there in my friend's bathroom. I kept looking at her panties and would visualize her sweet ass in them. It didn't take long for me to blow a huge load on his bathtub.
When I came to my senses, I cleaned up (easy to do, just turn on the shower). This is what started my panty fetish. I kept those panties and jacked off many times to them. I would cum on them time and time and time again, till they were no good anymore. Then I would go back to his house and take some fresh ones. But they had to be used. I had to smell that pungent crotch area. All I can do now is fantasize; she's a lesbian now. Too bad I can't take both of their panties.