I had stopped at a gas station to fill up with gas and went around back to a two stall bathroom and a sink. I was sitting on the toilet and noticed about a two inch diameter hole in the stall wall.
A few minutes later the stall door next to me opened and someone entered the stall. In about a minute I saw a soft penis sticking through the hole and it moved as if the owner of the penis was jiggling it. I became curious and touched the underneath of the head in kind of a tickling fashion with my index finger. Soon I was massaging the penis head with my fingers and thumb and the penis began to achieve an erection.
I sat on the toilet massaging and stroking it lightly for another five minutes, observing the veins and purple head. Every now and then I would hear him sigh and moan. Suddenly he blurted out to stop teasing him with my caressing and begged me to jack him off. I stood up and with my right hand I took a firm grip on his cock and began jerking him off. I could see his two hands grasping the top of the stall wall as I jerked him and he was moaning and thrusting his cock into my hand.
In a few minutes he shot ropes of his cum onto the floor with his erection becoming limp quite quickly. I exited my stall and hit the sink washing my cum (his) covered hand. As I left the bathroom he said 'Heh, thanks man'. I sat outside for thirty minutes, several different men went in and left but he never did. I guess he was returning my favor to others.