This happened a few years ago when I was just 18.
There was a gossip once in, or just after, high school that a girl (18yo at the time) from an other class was thinking of me while masturbating. I am really tall and she thought it would correlate with dick size. She had a really big booty for her age and she thought that only a tall big dick guy could reach her pussy and pleasure her right. The gossip got so bad that we had to sit down and talk about it so I could here the whole story. She was afraid that she was in trouble with her big ass.
I thought it was cute and I really like a big ass anyway so we tested her theory. She was not disappointed by my size and I was very happy with her ass. She was just between skinny and chubby with her ass already on the chubby side. Her big ass even helped a bit during doggy because I sometimes go to deep and run out of pussy in that position. With her it was just right. It was really good and we experimented a lot that time.