Yes, with my high school girlfriend… We'd park at night on the long gravel driveway leading to my house, and she'd lower her seat so it was almost like being in bed. Before we'd gotten to the stage of being naked together and masturbating each other, she liked for me to lie on top of her while we kissed and necked.
The first time I came in my pants, lying on top of her, my hips had started moving by themselves, and pressing my cock into her belly through my pants and her dress. I asked her if this was OK, and she whispered that it was, but neither of us expected me to cum—a LOT—into my pants, just a few seconds later.
It would have been nice to have her hold me while the orgasm passed, but I rolled off of her in seconds, afraid that my cum might soak through and stain her dress. She laughed and said she thought it was sweet, that I'd had a climax with her. But then there was the dilemma of what to do so what had happened wouldn't be obvious when I walked in, at my home, later on.
It was really dark out. I asked her to wait inside the car, as I stepped out, went behind the car, kicked off my shoes, and then pulled off my jeans and wet briefs, using the remaining dry surfaces in the briefs to wipe off my cock. Nothing like being naked from the waist down just a stone's throw from your home, with lights in the windows.
I got dressed again without my underwear, hoping that my damp-on-the-inside pants (and my jacket, which didn't come down far enough) would be adequate camouflage.
If my girlfriend was peeking while I stripped outside the car, she was good at stifling what would otherwise have been her characteristic giggles.