Oh, what a day for blogfodder.
If you find yourself so overcome (eh hum) with sexual urges and feel you must pull over on a busy street to masturbate, it's wise not to park beside a tall building, thereby giving the building's occupants a clear view of your solo act. It's also not especially wise to park illegally, which attracts even more attention. While not absolutely necessary, it's in good taste to close your sunroof.

If only I hadn't been so traumatized by the sight, while I was standing at the window taking my short morning break, I would have opened the window and shouted down something at the fool, like "You'll go blind!" The moron finished the act and drove away, according to what my co-worker reported after I collapsed in my chair screaming "OH MY GOSH! WHAT AN IDIOT!" The co-worker saw "something white" in his lap, but as the view from his window wasn't as "good" as mine, he couldn't tell exactly what that was -- perhaps a clean-up cloth (ARGHHHHHHHHHHH! Well, I suppose if you're prone to such abrupt sessions along the road, it's best to carry tissues, towels, etc.).

The only thing I've seen that's dumber than this was the time in grad school when we were sitting in class and some nitwit guy walked up to the classroom window and peed against the side of the building. We sat there appalled, but the teacher resumed her lecture on some obscure bit of 18th century literature almost immediately. While I assume the pee-er didn't realize there was a class on the other side of the window, he was right along a frequently traveled sidewalk and very much in the middle of what I'd call a public area. And it only would have taken a few seconds more to walk INSIDE the building to the restroom.