When having sexy with a large breasted girl the rhythmatic thrust causes her breast to slap together repeatedly. This can be affected by the size of the breast and power of the thrust. Best results achieved when ther girl is 34DD cup size or bigger and in the missionary or cowgirl position.
Samantha - So what's position does your boyfriend like best?
Jane - Well, I prefer doggy, but he's a breast guy so he likes when I get on top and pogo stick his dick. He says it makes for a nice Titty Clap.