I was 18 at the time.
I was a late starter when it came to sex so I had never gone any further than kissing a girl when I went to stay with my friend's family for the week during the holidays.
After I arrived we were just hanging out watching movies when I needed to use the bathroom. Whilst I was in there I noticed that there was a laundry basket in the bathroom, and it suddenly occurred to me that it may contain his very cute 16 year old sister's dirty clothes. I'd always been very intrigued to see and touch something that had been so close to a girl's pussy and breasts, and had heard that the smell of pussy could be very erotic, so I always wanted to find out for myself what it was like. I have no sister myself and must admit that several times I had considered smelling my mom's dirty panties just to see what it was like but it just felt too creepy and I knew I would regret it so I never did it.
My cock was beginning to harden as I realized I may finally get to find out, but I knew my friend was waiting so when I finished peeing I took a quick look in the basket and was happy to see some of what were clearly his sister's worn clothes inside. I closed the basket and went back to my friend, but my mind was constantly on what delights could be waiting for me in that basket.
I patiently waited until the following morning and as luck would have it his sister was showering when we woke up. I told my friend that I really needed a shower so he said I should go in next. When she was finished I grabbed my towel and went into the bathroom and locked the door. It sounds silly now but at the time my heart was racing and my cock was already growing hard so I turned on the shower and checked again that the door was properly locked. I then took off my clothes and excitedly opened the laundry basket. Yes! At the very top of the pile there was a small pair of black cotton panties with pink spots and trim.
I picked them up and felt the material, my hands shaking as I imagined my friend's hot sister wearing these sexy panties, pressed close to her lovely young pussy and firm ass. I suddenly noticed that they felt warm, and it occurred to me that she had probably been wearing them all the previous day, had slept in them all night, and then only just removed them about ten minutes previously when she took her shower. I couldn't believe my luck that I had these sexy panties in my hand, warm and fresh off her pussy.
I could wait no longer so I opened the panties so I could look inside, and figured out that the thicker patch of material in the crotch area must be where her pussy is in contact while she is wearing them (I had never looked at a pair of panties up close before). This was confirmed to me when I saw some pale yellowish staining in this area, as well as a small dark patch which was clearly still wet, which I guess was probably fresh pee from after she had used the toilet that morning. I could notice an unusual (to me at the time) smell coming from her panties already and my cock was rock hard, but eager not to waste my opportunity with a fresh pair of warm, wet panties, I rubbed the crotch of her panties all over the shaft of my cock and particularly the head. It was such a turn on knowing that what was now touching my hard cock had only minutes previously been in contact with a sexy young girl's pussy, collecting her juices and female scent for a whole day and a night.
Now it was time. Half expecting to be disappointed I lifted the panties to my nose and touched the stained crotch area to my nostrils and inhaled deeply. Whatever I had been expecting I had definitely not expected the smell to be so... strong. A powerful odor filled my nostrils and mouth and I have to admit my first reaction wasn't entirely positive-there was more than a hint of the cliche fishy smell that I had been told was just a myth. Feeling overpowered by this intoxicating scent I took the panties away from my nose and took a breath. To be honest I was feeling a little bit disappointed, but my cock was telling me otherwise, it was rock solid and throbbing away and I could actually see precum being produced at the top. I remembered that this overwhelming smell had been created by the pussy of such a hot girl and I suddenly knew that I loved it.
I lifted the panties back to my nose and took another long, deep sniff and this time I was completely intoxicated by the pungent, fishy yet entirely feminine, musky and deeply sexual scent. I thought of this smell coming from her pussy and put my hand around my hard cock, which felt incredibly sensitive, and within a few strokes I came harder than I have ever cum before or since, even from sex. I was kneeling on the bathroom floor and my cum shot out thick ropes high above my head and it landed all over my thighs and the floor.
I quickly cleaned up, took another long sniff of that wonderful aroma and replaced the panties. I made sure my shower was quick and when I finished I had to have another good sniff of her panties and made sure I replaced them on the top of the pile as I found them. I was amazed how that smell lingered in my nostrils for the rest of the day, I was even quite concerned that people may smell it on me because for the entire day I could still smell her pussy wherever I went. I felt a kind of horny guilt whenever I spoke to my friend's sister that day, knowing that I could smell her wonderful pussy that was only inches away from me, hidden from my view under her skirt.
I repeated this every morning until the end of my stay, always trying to get in the bathroom straight after her so I could get the panties as fresh from her body as possible. Sadly I have never since smelled panties that drove me as crazy as hers did.