I love this site!
This happened to me about a week ago.
I was reading stories on www.solotouch.com, and jacking, when my sister-in-law came over. She walked in without me knowing and was standing at my office door watching me jackoff.
She startled me by saying, 'That looks like fun!'
I stopped immediately, not knowing what to day or to do. She said for me to not stop because she had never witnessed a man jacking before and that it turned her on. I asked her if she would like to join me. I knew that she masturbated when she was young, because my wife told me that she did quite often at night because she could hear her.
She had huge tits and a nice ass, and I have jacked off thinking about her, before. What happened next was great!
She stripped off and I couldn't believe that her pussy was shaved. She started rubbing her clit and I resumed jacking. As she got nearer to cumming, she got very vocal and told me to suck her tits. As I sucked her tits, she started cumming and told me to cum on her tits.
I stood back and shot a load as instructed. She finished and licked some of the cum off of her tits. This was a big turn on for me. We got dressed and then talked for a while and made plans to do it again.