Two Part Story.
Me and my wife were visiting her family.
Her sister is divorced and has two sons. They are living in a three bedroom apartment.
Due to lack of sleeping space, her sister used additional mattress in her bedroom leaving the bed for us. The mattress was located next to bed, around two feet away on my side of bed the only piece of floor it could fit, slightly lower than bed mattress. My wife on the other side of bed as usual -- on my right hand side.
There was a dim light from the small outlet night lamp that gave some visibility.
I always sleep naked so me and wife went to bed first. Her sister came later in her pj.
For a long time I fantasized about being "accidentally" caught naked by her so while there was a good configuration I decided to give it a try tonight not really counting on something to happen.
I was turning left to right staying awake as my exhibitionist imagination did not let me sleep.
In about an hour, pretending to be asleep I started to switch positions to "involuntarily" remove covers.
I was now laying three feet from my wife's sister in the nude, thoughts racing about what I am doing.
All the thinking of a chance of my wife's sister seeing me that way made me hard. With my eyes closed I pictured my nudity and arousal on display.
Then I heard her gasp. I knew she saw me!
Lying for a moment on my back I decided to go all the way and slowly raised one knee and slightly turned left towards her so she got better view and then did not move to let her have a good, long look at my exposed hard-on in every deatil.
I really enjoyed the moment as I had never dreamed of showing her a hard cock at full mast. That was my bonus. All sexual excitement clearly visible.
I felt some precum coming out. I was so aroused that I barely controlled my breathing.
The only reason I did not open my eyes and looking at her start to openly masturbate for her was my wife on another side of bed.
How much i wanted to do that at the moment. The shameless sexual performance while she watches would be something to remember and "regret" for the rest of life.
I do not know if she was looking all that time but was afraid to move. I did not want to give a tiniest hint that I was not asleep.
After a while she turned to the wall, I guess to avoid being caught and moment later I turned and covered myself still pretending to be asleep.
In the lazy morning we hesitated to get out of beds. My wife went to bathroom first so I asked if SHE was going next.
She asked "Why?" and I said because I wait until she leaves.
She then asked if I sleep without panties. I saw her trying to hide a smile and answered "Yes".
She then left to the bathroom and nothing was ever said. She does not know that I know.
I feel so good knowing that I was finally able to expose myself to her, especially my full hard arousal.
After that night, every time we met I hoped she was undressing me in her mind!
Couple years later I was there without wife.