I came in my pants
This happened 1 year ago. I was 21 at the time.
I had come home to visit my dad and stepmom and my little step sister. I guess I hadn't had an orgasm in awhile, or maybe I dont have an excuse but it still both weirds me out and turns me on.
We had gone to the lake that day and were all wet and warm from the sun. Mom has a small hatchback so we had the car packed up and everything fit on the way there, but when we piled it all back into the car we couldn't get the chairs to fit so we put two In the back seat. No big deal my lil step sis was just gonna ride back sitting in my lap. I climb in shirtless with only my damp swim trunks on, while she climbed onto my lap wearing her little bikini. I had watched her earlier and admired her tan skin and firm little butt, and I have to admit that this was the first time that I noticed her body in any way sexual. Well she when she crawled across my lap I noticed her swim bottoms had bunched up Into her crack, exposing one of her cheeks.
I felt my cock jump a little as she turned and scrambled to get her butt into my lap. I thought omg no please dont get a boner right now. She settled down and I could feel her cold damp buttcheeks against my thigh, which causes more blood to rush to my groin. My cock swelled until it was up against her crotch. She kept switching from one thigh to the other kinda grinding herself on my thighs as my cock became engorged. I didnt know what to do but at least she didnt seem to notice.
At one point she leaned forward to talk to the folks and she was straddling my thigh with her little wedgie butt pointing back at me. My cock was pressed hard against my other thigh and Instictivly reached down trying to relieve the pressure. I reached down and grabbed my cock over my swim shorts and felt the heat of my hand. I couldn't help it. She was leaned all the way forward with her belly on my thigh and her little snatch was visible peeking out of her wedgied swimsuit. I started stroking my cock through my shorts while I imagined pulling her bikini bottom to the side, pulling my cock out and sliding it up the crack of her butt under her bikini.
It was so hot and I was playing a dangerous game. I kept stroking my cock through my shorts and felt the blood build in my groin. Just then she rolls back up and plants her butt down onto my cock that is engorged against my leg. I grab her left thigh with one hand and the seat edge with the other as I feel a huge surge if cum rising up out of me. She is leaning back wiggling her butt looking up at me as I shoot a huge jet of cum into my pants and down my leg, then another and another.. my God I must have filled 4 shot glasses, as a good portion had shot out the edge of my pant leg and onto the floor below. We sat like that for another 10 minutes, when we got home I grabbed a towel, put it around me and ran inside the house to change. I'm still not sure how much cum I got all over the back seat and floor of the car. But my balls ache just thinking about it right now.