It was 8am on a Wednesday, and Mom and I were exercising in the basement. I religiously worked out five mornings a week, and she was always right there with me. We started with a run on our two treadmills. Mom's industrial-strength sports bra didn't completely restrain the bounce of her D-cup boobs, which I loved to watch. She didn't seem to notice.

Mom's big tits were a present from Dad for her thirtieth birthday. She told him she didn't want to go through her whole life with tiny A-cup boobs, and he was happy to pay for a boob job. At the time she was also becoming overweight, as...