As long as I started the thread, here's mine:With a girl, we were in the coat closet of a conference room in our campus center building. There weren't any people nearby, but it was lots of fun knowing that we could get caught, and all.
By myself, hmm... don't think I'm totally sick, please:
my favorite is the drivethrough at Taco Bell. It was dark, I was about 2 cars from ordering, thought that I had a little time, and went at it. That totally ruled.
Other than that, standing at a urinal at work, on a school bus while it was transporting me, while driving to work... I'm sure there are others that I can't think of.