This happened when I got my first pad and my sister came over to help. I was 21 at the time, she was 24. I am 6' 200lbs ,5.5" cock. She is 5'2" about 165 lbs, big tits.
I got my new pad and my sister came over to help me unpack. I got some cold ones and we got unpacking. She was really scrubbing and cleaning while I unboxed stuff. It was a really hot day and she was wearing shorts and a tank top.
After a while we took a beer break. She was standing there hair all messy sweating buckets. She put the beer to her forehead and it dripped down her chest a bit, I watched and felt a movement in my pants. She had huge tits I'd say 38D at least. I was staring too long when she cracked a smile and said look much! Busted. I said it's been a while since I had seen any tits. Without another word she lifted her top. She was wearing a boring bra but boob flesh all over. Then she reached back and took her bra off. I couldn't believe it my eyes were wide open.
They were big and white with nice big nipples. I got rock hard. She looked down and saw the hard on and had a big laugh. When she laughed her tits bounced up and down. We were going to go out for food. I said well I have to have a shower, ok she said.
I walked into my bathroom ran the water, really wanting to jerk off. I was naked and ready to get in with my cock at full attention. I got in when I heard the door, my sister walked in the bathroom. She pulled the curtain aside. There I was full hard on and she was still topless. She dropped her shorts got in the shower. She said turn around, she scrubbed my back. Then she pressed her tits against my back, she reached around me and began stroking me. She whispered, tell me what you would do if I wasn't your sister. I imagined all sorts of things and talked dirty. She began stroking really fast, I started cumming hard and long ropes all over!