My wife Sue and I were staying at my mother-in-law's house for a week for vacation. Her 24-year-old younger sister would be there too. The house was small and only had one bathroom. We worked out the shower schedule and all that, so that wasn't the issue. The issue came at night if two or more people needed to use the bathroom at once.
The second night there I woke up and had to go. I also had a major boner. So, I sat on the toilet, waiting for my cock to go down so I could pee. I often sit to pee so that I'm sure not to miss the toilet and mess up the bathroom. I really didn't want to pee all over my mother-in-law's toilet. There isn't a window in the bathroom and it's really dark. So, when I heard the door open and someone else come in, I froze.
At first, I thought it was Sue, but I soon figured out it was her sister Cindy. She literally sat directly on my rigid cock. I reached up to cover her mouth so she wouldn't scream. In doing so, I brushed against her big boobs. They were way bigger than Sue's, medium tits. I cover her mouth and whispered in her ear.
"Cindy. It's me, Tom. Don't freak out."
"Tom? What are you doing?" Cindy asked. She's cute but not very bright.
"What do you think I came in to pee," I stage whispered.
"Sitting down?" she asked.
"Yes. I didn't want to pee all over your mom's toilet. But I had an erection so I was waiting for it to go down," I explained.
"Well, that's not gonna happen. Your cock is inside me."
"Trust me. I know," I said, feeling my cock getting harder and bigger.
"Well, I can't wait. I have to pee," she said and suddenly I felt her piss running over my cock and down into the toilet.
Her warm pee triggered my body to respond in kind and I started shooting my urine up inside my sister-in-law. It felt amazing. I have a really powerful stream and it was really shooting up there. I also felt it roll back down and out of Cindy's cunt too.
"Holy shit, Tom. Oh, fuck, I think you're gonna make me come," Cindy said and started rubbing her clit.
I reached up inside her shirt and grabbed her big, braless, tits. When I started pinching her hard, plump nipples, she lost it and exploded all over my cock.
After her orgasm, she got off, tore off her shirt, spun around to face me and climbed back on my still hard cock and started riding me. She told me to suck her tits, which I gladly did. Too bad it was so dark I'd love to see what her tits looked like.
By now I was ready to shoot and told her, thinking she'd get off and simply jack me off to finish me or make me do it, but she stayed on my cock. I couldn't hold back anymore and shot my load into my sister-in-law.
She lifted my head, gave me a deep French kiss and said, "Best piss I've ever had." Then got up, wiped herself and went back to her room.
The next night I got up again and went into the bathroom. I wasn't going to take the chance and decided to stand this time. As I got closer, I felt someone sitting on the toilet.