My sister let me feel her breast.
Many years ago when I was about 17 during a Christmas holiday I went upstairs to use the bathroom. My sister was coming out of the bathroom. She was wearing a very tight turtleneck sweater and it was obvious that she wasn't wearing a bra. Her nipples were hard and poking out of her top. She smiled at me and said 'How are you, little brother?' and gave me a hug. I immediately got very hard and she must have felt it pressing against her thigh because she said 'What is it you have there?' as she pressed against me. I was embarrassed, but too turned-on to really care, so I grabbed her breast and rubbed my thumb against her nipple and said 'What is it that YOU have there?!' She giggled and let me feel her for a bit then pushed me away and said she better get back downstairs before her husband wondered where she was. Nothing more happened that day but it certainly gave me plenty of fuel for my fantasies many nights. Other things have happened. If you'd like to hear about them please comment.