I have dived (head first) topless and nude and it hurts when my breasts hit the water. I learned that when I was a teenager. I only dive with a tight fitting suit. Jumping topless, feet first off moderate (for me anyway) 25 foot cliffs into deep water doesn't hurt like diving head first does probably because the feet break up the surface of the water and make for a softer impact on the breasts.
I've often wondered if girls had anything that hurts when diving or jumping into the water. For me it's my balls. It hurts when I jump into the water and they get slapped. I don't know if it's by the water or them getting slammed up against my body. My other problem came into existence when I was 10 and had my tonsils out. The water getting forced up my nose really hurt so I look like a freak when I go swimming holding my nose with one hand and my balls with the other to jump in.
Actually I wondered if you got water forced into your vagina when jumping in feet first and does that feel bad or good if it does happen.
The girl we always called my sis when we were hitting the bars had good sized boobs and she looked neat standing in a pool naked with them floating up and down in front of her. She used to make them bob up and down to tantalize the other guy who was with us. He was hot for her but his wife was always there because it was their pool. They had a floating chair that she used to get into, laying back nearly flat. I used to slip up on top of her and slide up and down against her just to bug him. For some reason she didn't turn me on even though she was beautiful so I never got an erection doing that but it sure got to him seeing us do it.