When I was back in college, I was enrolled in an art/sketch course. Towards the end of the semester the instructor told us that someone would be coming in to participate in a nude drawing. Just hearing about it got me a little excited, and I couldn't wait to see what the guy looked like.
The next Monday was when it was going to start, and when everyone was ready the guy came in the room in a bathrobe, then dropped it leaving himself completely naked in front of us. He laid down on the bench that was set up and we started drawing. I was trying to do my best, but I wasn't able to focus that well. The guy had a fantastic build and was completely shaved, and had a good looking cock as well.
About 20 minutes went by and we were well into our drawings, and all of a sudden his penis started to twitch and grow. I guess it was the excitement from being naked in front of a group, but in no time he had a full blown erection. He tried to ignore it, but it wasn't going anywhere. If anything, it got harder as time went on. Eventually the instructor came over and he whispered in her ear, then grabbed his robe and left the room. She told us we were going to take a short break, and about five minutes later he came back, penis now soft and floppy again. I knew that he told her he needed to masturbate, and it was all I could think about. I could just picture him in the bathroom, standing there naked, stroking his big thick cock, needing to cum. I bet it felt fantastic. I could just see him rising up on his tippy toes, his burning hot penis shooting cum all over the place, making him grunt and growl like a wild animal. Oh how I wished he would have rubbed it out right there, showing us all how he loved to masturbate.
By the time the class was over my crotch was soaking wet. I didn't even bother going to my next class, I just went back to my dorm room and stripped naked, having an unbelievable masturbation session for the afternoon. Using my vibrator I came four times in a row, leaving a big wet spot on my bed. My pussy was tingling for a good hour after my last orgasm. All I could do was roll over and fall asleep, then masturbate again when I woke back up.
The next day he came back for one more session, and even though he didn't get an erection that time (did he masturbate before he came out?), I repeated myself afterwards.