Although this thread started about j/o, it went on to fucking, so here my first ever, which I'll never forget.
I was 16, riding in the subway at rush hour back from swimming class, shorts, freeballing, t-shirt, guy in a suit in front of me started to rub his ass into my crotch, car got very full, we were in the back, he hid his front with his attaché case, opened his belt, exposed his ass and I went in in no time, took me less than a minute to shoot a load between his thighs. People around never noticed. When I was to exit he followed me, sun was already down, we found a dark alley, and this time we took our time until both came gloriously. We tried to meet another time, but the thrill was gone, we just had a beer and wished each other good luck.