About 10 years ago, while I was at University, I lived with my then girlfriend and her mother and older sister. It was a very small house and the layout of the rooms made for little privacy. The 3 of them were comfortable being naked in front of each other when it was just them living there. Her sister and mom initially made adjustments when I was around, but it always felt like it was only a matter of time before the privacy levels were gone. The wall between our bedroom and her sisters was paper thin, I used to love hearing her moan and orgasm during sex.
After about 6 months of living there, I was heading back to the house and was messaging the girlfriend about her plans for the evening. She told me she going to have a quick shower then head out to see her friends. Upon arrival, I dropped my gear off in our bedroom and could hear the shower going in the bathroom across the hall. Without hesitation, I went through the door, took off all my clothes, opened the shower door and before I could finish saying hello, I realized I had made a mistake. Turned out my girlfriend had already left and it was now her sister in there in the shower. She let out a little startled shriek. We both froze, I couldn't help but give her body a look from head to toe. As I saw her eyes, I could see she was doing the same, giving my cock a decent stare. She had smaller breasts than her sister, but they were perky with huge light pink nipples. I got a good look at her nice black bush which was shaped into a very wide rectangle. After what seemed like a age, but was probably only a few seconds, she turned away in embarrassment and I apologized profusely before running out back into the bedroom. I apologized again when she was out and explained I thought it was her sister. She was totally cool with it. When I told my girlfriend, she (and her mum) thought it was the funniest thing ever and things definitely changed completely after this day. Her sister no longer always ensured she was covered up when she went from the shower to her bedroom or vice versa. It really wasn't that strange to get a quick glimpse of nipple and bush as she walked past, in fact a couple of times she walked passed with just a towel on her head. The more she did this the more comfortable and lazy I got, and I started to often get caught walking naked to and from the shower or bathroom by both the sister and mother.
Pretty soon after this, the boundaries seem to drop completely and no one cared at all. Her sister would come into the bathroom and talk to us while we both showered and got changed, and would comfortably strip off and shower in front of me. Not long after this, I got a full frontal view of the mom. The bathroom had 2 entry doors - one in direct view from our bedroom and one straight through on the other side directly to her mothers bedroom. While the door on our side was open, her mom entered from her side and stood in front of the mirror completely naked. She was actually in better shape than I ever would have thought. Her breasts were drooping a bit to the sides but still looked great with her pink nipples. She had the biggest bush I have ever seen, so thick and lush in a huge triangle shape that was starting to run down her thighs. Only got to see her naked the one time.
Its funny, I always got a little thrill out of being seen with my cock out by her family, I certainly put myself in situations knowing I would be caught and enjoyed it. It never ventured into anything sexual, once her sister walked in on us in the shower, and I had a massive erection and she clearly was embarrassed and left the room immediately. I found out many years later, after the girlfriend and I had moved out to our own place, that her mother had also seen my erect cock while we were there. She had come to get us for something while we were in our room in the middle of the day, and seeing as our door was slightly ajar she went to go straight in. The girlfriend was lying on top of me in the 69 position, the mom got the nice close front on view of my erect cock in her daughters mouth before discreetly leaving us along. I asked about how her mom brought it up with her, she said they were talking about penis and she was commenting on mine
I moved on from that relationship a few years ago, but have clearly treasured that time I lived there and seeing all the family in their glory and them seeing me in mine, it was a thrill.