"Pervert on a bus"

I was on my way to university. I took a public bus which was almost empty since it was an early morning. I was sitting two rows from the back, facing the direction the bus was going. There was an old man sitting on the back seat, I didn't notice him at first. Then he stood up and went to stand next to the door of the bus (and next to me). I noticed that he turned at me a few times but I didn't want to pay any attention to him, I was hoping that he will get out on the next stop. But he decided to sit on the side, one row in front of me, facing me. I was looking straight with no emotions since I didn't want any interaction with him. But I saw that he was watching me. Then I took a glimpse that he was doing something with his hands, but I didn't want to believe it. Finally I decided to look at him. He was jerking off at me. Then his hand movements stopped and I saw the tip of his penis through his open zipper. He jumped and started to put his dick back into his pants. I immediately got out of the bus on the next stop but I felt very disgusted by what happened. Sadly, a few people that saw it didn't do anything