I have thought that he may have before, but I know for a fact he did this time. (Note that my dad and I have never discussed anything sex related except a couple of questions I have had about my penis)
I am nineteen years old and I just returned home from college for the summer, and this happened a couple of weeks after I got back.
I had been home all day cleaning in my room, and I decided it was time to take a shower. I went and got all of my clothes, towel and wash cloth ready and started to undress. As I was undressing, I began to get an erection (which is not too unusual when I am fixing to shower). I immediately decided to take care of it since I was home alone. I then went to my room and dug through my things to find a bottle of lube I had carried back home with me from my apartment. I then went to the bathroom, sat down on the toilet and began to stroke. After a moment, I decided that I would turn the water on in the tub and let it be getting hot. After that I returned to the toilet and resumed my intense stroking.
Between the noise of the water hitting the tub, the radio, and the sound of my lubed hand running over my extremely hard dick, I was completely caught in the moment. I had been stroking for about two or three minutes and was really into my session when all of a sudden I heard my dad say 'Hey!', I immediately looked out the bathroom door, (which I didn't close because I was home alone), and I saw him standing in the hallway looking in. I quickly shut the door and replied that I was fixing to get a shower. He then asked if there was anything to drink in the house, as if he hadn't seen anything, which I knew he had. In return I went to the door and stuck my head out and asked him not to say anything about what he saw, but he just turned around and went to the kitchen.
I then went and put on my clothes and went to talk to him. At first, I found him something to drink, then once we both were quiet, I asked him again to please not say anything. He said 'why?', and I said 'because you just caught me doing something I really don't want mom to know about,' he simply looked at me and said something like well you always want me to stay quiet about something. I thought a second and looked him in the eyes and said,'Please Dad, I mean YOU DO IT TOO, so please don't say anything.' (and I knew he did cause sometimes when I would do his laundry, I would find I pair of his briefs matted together with cum, that he used to clean up with). After I said that, he just looked at me and I went back to the bathroom and finished my session, and it was one of the best I have ever had, knowing that my dad just caught me doing something that I know he does as well. After I finished, I took my shower and went and watched t.v. with my Dad.
After a few minutes, he went to the bathroom and was in there a good while. I heard the cabinet door where my mom keeps her hair products and lotions close and then my dad came back and watched t.v. again. I guess he may have gotten excited to know that I knew he did the same thing, but to this day, he has still not mentioned the incident again.
I think I may sometime soon though, just to see what he says!