My son was using it and he wasn't very neat. I had called him and told him I was letting a friend use the apartment tonight."Okay Dad, I'll stay away....I'll see you later." We gave each other a lot of space.Five minutes after five there was a knock at the door. There were two very cute young ladies. I recognized Kat from her picture. She was five feet, six inches tall and shaped nicely. Her blonde hair was piled on top of her head. Not voluptuous, but desirable looking. Small, nicely shaped. "Whaooooshit!" Becky pushed me back at the hips staring down. I looked down. I was still in boxers, and the button on the front of the pee slit wasn't buttoned. My erection had found the hole and said hello. I had never seen it that big before. The head looked swelled. She had felt it against her leg and it had gotten her attention. "What the fuck is that out for?!" She said in a hushed and panicked tone. I searched for something to say, to explain. My cock was pointing directly at her, just. Nothing.Maybe I'd imagined it. Maybe it was from the room above and the acoustics in the sparsely decorated room were playing tricks on me. Then some more creaks of a bed. There was definitely activity next door. I stole from under the covers, dragged the desk chair to the wall and sat. Leaning into the wall I pressed my ear to its surface and adjusted the angle to hear more clearly. It's not the most comfortable position in the world but it works.I waited for more sounds but there were none. I slid them in and out, timed perfectly with my dad's rising and falling grip on his thick erection. Oh heavens, how I wanted to mount him and have him nibble my nipples and squeeze my tits. I spread my legs a bit farther and leaned forward onto the door frame, getting closer and closer to the cracked door when suddenly I was going too far and my hand slipped off the support. I went crashed through the door and landed with a hard thud on the floor. My Dad stood up quickly, not sure whether to x.