One day, not too long ago, I walked over to my best friend's house. We are really close, so usually when we go over to each others' houses we just walk in. I went in the back door and took off my shoes, but since the downstairs was quiet and I heard a TV on upstairs, I figured that's where he was. When I got near the top of the stairs though, I could see his mother in the bathroom. She was completely naked except for her underwear down around her right foot, and her left was on the edge of the tub. Her back was to the door and I could see that she was masturbating with one hand and squeezing her boobs with the other.
I never really thought of her as being attractive because she was overweight, but seeing her without any clothes on was different and got me pretty horny. She was really working herself, talking dirty and moaning her husband's name, saying to fuck her wet cunt and to make her cum. After a few minutes, she got down on her back and put her feet on the tub and started fingering herself with both hands. She was rocking back and forth, and when she came her toes spread apart and then clenched back down over and over again.
When she was still on the floor, she grabbed her underwear and wiped herself off with them, then tossed then into the dirty clothes basket. When she was catching her breath, I snuck back downstairs to the back door, opened it and closed it and called out my friend's name. She sounded kind of scared when she told me to hold on and I could hear her hurry down the hallway, then she came down still barefoot with her robe and sweatpants on. She told me that she was sleeping and I startled her, but that my friend had gone to the food store with his father and that I could wait in his room if I wanted.
I told her I needed to use the bathroom, and when I went in, I saw her underwear. I grabbed them and they were still wet, which got my penis rock hard in no time. I dropped my pants and sat down, smelling them and feeling them while stroking myself. I then licked them, and as soon as I tasted her cum, I blew the biggest load of my life. I was so horny, I kept stroking with her underwear under my nose and came again a couple of minutes later.
So far no one has ever found out anything that happened, but every time I have masturbated since then I have thought about that.