>>24638544 (OP)
When I was 19 years old and in university I always used to go to the university library to the private reading rooms to jerk off. I'd close the door to the reading room, look up erotic fiction on my laptop, and read until I was ready to pop. Then I'd cum in my briefs and finish up. The crotch of my pants never got stained, so when I left the reading room and then left the library nobody was ever the wiser.