I'm not an exibitionist, so this experience was quite drastic from my norm...
I'm an 18-year-old college male who lives away from home. Whenever I have a break that's at least three days long, I drive the 300 some-odd miles to be with my family. This Spring Break my University gave a five-day break, and as soon as my classes were finished I jumped in my car and headed home.
Over the course of the drive, I had been lightly stroking my penis, never really paying to much attention to it, more out of having something to play with rather than having an orgasm. The weather and traffic was quite bad, and while on a main interstate I came almost to a stand-still in heavy traffic.
While waiting, my penis got incredibly hard, and I suddenly felt really horny. Looking in my glove compartment, I grabbed several napkins, and unzipped my pants. I'm not that large, only five-and-a-half inches, but it is long enough for me to stroke while sitting down. Using my right hand to drive and my left to stroke, I slowly brought myself higher and higher. Several times I had to stop, because I was afraid that the people in the cars next to me would see me and know what I was doing.
After several such halts in the action, the traffic stopped, and I started stroking as fast as I could and I came with a loud grunt. My facial expression probably was apparent to the driver in front, if they happened to be looking in the rear-view mirror.
I quickly cleaned up, put my Precious away, and when that was over with, traffic cleared away, I continued on my way home, to another session in my own bed.