To start out, my mom has a normal 9-5 job, and my stepdad works third shift. They don't get to see a ton of each other, just when he gets home in the morning, before he leaves at night and on the weekends. I guess that's why he needs to have a little 'release'.
When I come home from work in the afternoon, he is generally already asleep, but this day I got off an hour early. I walked in and called for him, but I didn't get a response. I went upstairs to see if he was already in bed, but he wasn't. I glanced in their room, and he was on the computer with his back mostly to me and he was naked, slowly stroking himself while watching porn with headphones on. To back up a little, I have heard him and my mom before, and it always seems like she is really into it, and now I know why. His penis is enormous. It had to be somewhere around 9-10 inches and thick. Whenever he would let go of it, it would spring back and slap him in his belly.
I have never thought of any other guy in any sexual way, but seeing him like this, I was getting hard in a hurry. I made a little noise in the hallway but he didn't turn around, so I decided to go for it. I stripped down naked and started stroking watching his show. I tried to match his pace so I wouldn't blow too soon, but I was leaking precum pretty fast. I didn't see anything around, so I took one of my socks and slipped it on my penis and went back to my own jerk session. It must have been some sight; two guys right by each other, both naked, both masturbating like crazy, but one of them didn't know it.
We both took it kind of slow, but after a few minutes he started making noises and picked up his pace. He started squirming around in his chair so I knew he was going to cum, so I started stroking as fast as I could. Then, he let out a deep grunt and started cumming. I couldn't believe it, but when he came, it shot out like a fountain all over his chest. It must have been a half dozen thick, creamy squirts before it started running out over his hand. Even after all of this he didn't stop stroking and he didn't get soft. A couple more minutes went by, and then he leaned his head back and more started running out of his cum-covered penis. I couldn't believe that he came twice! I couldn't take it any more, so I let loose and filled the sock with my own hot sperm. I dropped to my knees and milked myself for all it was worth, squeezing out every drop I could. When he grabbed his towel and started wiping up, I knew I had to move, so I grabbed my clothes and tiptoed down to the basement, wearing nothing but that sock.
I sat down there naked, waiting him out for the next hour or so, and while I had the chance, I masturbated two more times, but this time I shot it in the sink. When it was the time that I normally got home, I got dressed and went back upstairs, but now he was sound asleep. I slipped into their bathroom and got into the clothes hamper, and buried a little bit was the towel. I opened it up and it was soaked with cum. Just seeing it got me hard again, so I masturbated one more time in their bathroom, dribbling out what little cum I had left, mixing it with his load.
By that time I was completely exhausted, so I went down and fell asleep on the couch. When he left that night, I tried to make everything seem normal, but all I could think about was the massive meat in his pants. I didn't masturbate again that night, but when I woke up the next day I stroked off to another great orgasm.