i had similar encounters back then.

Once when i took a bus home from school. It was the last seat at the last row of a bus. There was a guy sitting beside me. The guy asked for the time, and promptly answered by showing my watch. That's the only conversation i had.
And then, the guy beside me started to move suspiciously. I had my bag on my laps, and he seems to want to stuck his hand between my tighs and his.
anyway, i got freaked out and started stand up to walk to the front of the bus to wait for my next stop. It was still a few more stops away, but i don't care.

Another time was when in a crowded bus. We usually like to hold the seating rails instead of the hanging rails. So, i was standing facing the windows. At my back i can feel a guy standing very close and he is jutting his lil' bro at my back. I got uncomfortable. That time i was only 14, i think.
So, i changed my standing position and moves away from him.

There are lots of perverts in these public transportations. More so when its crowded. I've seen with my own eyes how some guy take advantage by nudging their arm on the girl's breast who is sitting beside him.

That's why, public transportation is such a nightmares for girls and women.