I was coming home early one day earlier this week so I took a midday bus home, which is usually very empty by the time it gets to my part of town. I had worn my favorite underwear that day.
I deliberately sat in the very back of the bus, and was playing with my cock through my open fly, first on top of my underwear, then with it pulled aside.
Eventually the bus emptied out enough in the back that I got out some lube (I had planned this) and some tissues, pulled my cock out completely and slowly started to jack off.
The bus stopped to pick up a passenger, an early twenties girl, a bit chubby, but a little cute. She couldn't see what I was doing since she sat towards the front which was lower than the back, and partly separated by a divider. She smiled, not having a clue at all what I was doing. I watched her sitting there as I jacked off and eventually came, then cleaned up. She got off the bus before me and smiled at me again as I left.