This just happened last summer. My parents were at work until 7. I had just gotten home from practice when I saw my sister Julia, who was about 15 or 16 at the time, and her friend Emily, who lived a few blocks away. They were lounging around the house, so I went upstairs and watched TV and stuff.
I came back downstairs and heard the two of them fooling around in our pool. It was hot, so I was wearing athletic shorts. I went out to see what they were doing, when I realized neither had anthing on. Anywhere. Not even a bikini or something.
I got an instant boner, and they looked up surprised. I hadn't seen her naked since we were little, and boy had she changed. It was hard to tell underwater, but she had a nice pair of what I think were Bs. Emily was much more mature, with Cs or something like that. I felt like my dick was chewing through my shorts.
They both said they thought I wouldn't come down for a while, and looked really embarrassed. They begged me not to tell mom and dad, and would reward me if I didn't. Overcome by hormones, I agreed, curiously.
They both pulled themselves out of the pool. They walked over to me and they looked amazing. Julia had nice big breasts with smallish areolas and little brownish nipples. She has blond hair, and was totally shaved. Emily had larger areolas and big pink tips, and a small strip of brown hair over her crack. Neither had any tanlines. I was in heaven.
Julia ran and locked the sliding door, boobs bouncing the whole way there. Emily came up to me with my noticable lump in my shorts. She said 'Someone's a little excited'. She grabbed my shorts and threw them in to the pool. I'm moderately sized, about 6 inches erect, and circumcized. Now I was trapped, in a pool with 2 hot teenage girls, and we were all naked. My dick felt like it would explode.
First, Emily grabbed my dick. I tried not to burst. 'Not bad', she said as she squeezed it. My sister came and touched it too. Emily took my hand and ran it over her breasts. They were so big, and soft, with rock hard points. Julia took my other hand and stuck it between her legs. She was wet down there, and it wasn't from the pool. Emily, who still had a hand, closed it over her left breast, and had me squeeeze it. She moaned and I almost lost it. All 3 of us sat down on the deck.
Now my dick was clearly throbbing in front of them, as they opened their legs to show their juicy folds. Emily told me to look closely, as I leaned in to see her lips. They were bright pink, as she started to tease them. She ran a finger up and down her crack, and pulled it out. She told me to taste it, as I opened my mouth. I sucked her finger, and felt her warmth along with the sweet taste. She put her finger back in and sighed as she continued probing herself. She flicked her rock-hard clit, a little pearl sticking. She sighed as I watched her go in and out with a few fingers, teasing her little bundle of nerves with the other. I looked over at my sister, who was getting hot too, and was playing with her lips, while twisting her little nipples.
Julia suddenly moaned loudly as her body went ridged. Emily soon followed, shuddering as her orgasm ripped through her. I just had to touch myself now, but Emily was too quick, and grabbed my hot, hard rod. With one touch, I exploded, making sure not to get any come on her. We all cleaned up and took a shower together, but never talked about it again.