Well, I grew up before internet. I remember in the early to mid 70's discovering that my penis was an object of great pleasure. Somewhere early on in that time I started feeling sorry for my dog, because he didn't have a left or right hand. So when it was just him and me in the house I would devote my left hand for him to hump on while the right hand was for me. We never did any more than that, but we did that a lot. It made quite an impression on me from the first time. I was amazed that cum started almost immediately and it never stopped. The amount was impressive. He also had explosive ejaculations that seemed to shoot a pretty good distance. I usually would sit in the bathroom because it was easy to clean up the tile. On several occasions he shot a load that hit my mouth as I sat there panting almost as much as he did. It never bothered me when that happened, I noted the taste was not horrible, swallowed it on down and that was that. Of course the most impressive thing was how big his cock would get.
After I became sexually active with girls in high school, I still had time to take care of my best friend. A couple of girls I ran with were wild as could be. I remember thinking if they ever got that doggy cock, it would be the last time I would get any. I also remember thinking if I could just watch my dog fucking their brains out it would be the most orgasmic thing I could ever do. It never happened but the mental image is powerful. Porn is too set up most of the time.
There's that. This began in my head, long before I ever saw any porn.