On the weekend I went to the 60th birthday for party my wife's boss at his home. He lives in this large older home and had a huge pool/hot tub patio bar.
The party was a strange mix of co-workers, neighbors, his extended family and a bunch of teenage grandchildren.
After having a few drinks, I went into the house to take a leak. The bathroom by the pool was occupied and I went down a hall looking for a bathroom and found one that was in between two bedrooms with a door into the hall and pocket doors into each bedroom. One room was a spare room and the other had been converted into a workout room with a weight machine and a mirror covered wall. The pocket door going into the weight room was off its track and jammed about 3/4's closed.
As I was using the toilet, I heard voices in the weight room. I looked in to see two of the teenage girls changing out of their bathing suits. From where I was, in the bathroom I could see them in the mirror as they stood around the corner.
One girl changed quickly and left to re-join the party. The other said she would be down in a moment but wanted to dry her hair. She pulled a blow-dryer from a sports bag and began to dry her hair while standing naked in front of the mirror.
She was short, wide hipped with medium (B cup?) sized breasts that had the tiniest nipples I have ever seen with long black hair and geeky glasses. Her bush was full and untrimmed. After a moment, she put the hair dryer down on a bench, leaving it running and closed and locked the door into the hall.
Returning to the bench she stood with one leg up on the bench with the other on the floor. With one hand I saw her clearly open her labia to expose her clitoris. With the other hand she began to quickly flick the tip of her clit with her index finger in an upside-down 'come here' movement. After a moment she started to rock her hips back and forth while sort of pressing the palm of the hand she was using to hold herself open with into her mound. When she came, she jerked her back into an arch and almost fell over as her foot slipped off bench. She stood there for a few seconds and then slid a finger into her crack and smelled and licked her finger.
The entire time this was going on she was looking at herself in the mirror and smiling. She then stepped out of my view and got dressed.
All of this took less than two minutes.
I had been standing in front of the sink ready to wash my hands when this started. I had a raging hard-on was thinking I could jerk-off into the sink when the bathroom door opened and she walked in.
I said that I was almost finished; I washed my hands and left the bathroom. As I left, she brushed her ass against my crotch as we passed each other in the doorway and I swear I almost came in my pants.
For the rest of the afternoon I kept my eye on her and kept thinking what she would say if she knew what I had seen.
That night, even after my wife and I had a quickie; I was still horny. I masturbated after she had fallen asleep and thought she did not know.
In the morning my wife asked me 'what had gotten into me' (in a nice way) as she told me she knew I had masturbated.
I told her what I had seen and at first she was a bit upset. Her problem was what would have happened if the girls had seen me watching them change of if the girl had walked in on me with my dick in my hand. This was at her boss's home and the girls in question were either his grand-daughters or nieces.
I asked he what she would have done if she had seen a 19 year old boy changing and jerking off and she admitted she would have watched and gotten turned on by it.
That afternoon we masturbated together, something we have not done in years.