When I was 13 or 14 I would ride the bus home from school because I lived in a rural area.
I rode the bus with a girl named Cory (name changed) who was a year younger than me.
One day she was wearing a white shirt that was a little too large and would hang down in the front when she bent over. One of the times that she did this I got a look down her shirt and saw her bra and the beautiful bounty within.
I had overheard her telling her friends that she was a b-cup if barely and she was wearing a bra that was just a little too small because they pushed her breasts out a bit.
I could just see the top of her nipples around the top of her bra because it was a lacy thing. I had to hide my erection all of the way home.
When I got home I laid down on the floor and started to rub my circumsized penis. I imagined her riding my cock and moaning as I slid within her. Soon I felt my orgasm coming on and when I ejaculated I shot almost to my chin.
Later at school one of our mutual friends said that she sometimes thought of me when she rubbed herself.