Many years ago I shared a flat with my then girlfriend (long since broken up!) called Hilary and her younger sister sister (Emma) lived close by. Both were early 20's. Hilary was a nurse and was in the habit of taking a bath when she got home, with which I often lent a helping hand
One evening Emma was round at the flat, and Hilary came in from work as usual, said hi to us both (watching TV) and went off to undress and have her bath. When I heard her go into the bathroom I thought to myself - just for a laugh I'll see how far I get with our usual bath routine with Emma here, not expecting to get very far at all. So I got up from the sofa and went into the bathroom just before she locked the door. She wondered what I wanted (with her sister being in the flat) but nevertheless took her dressing gown off and got into the bath. I suggested to her that it would be fun to try to embarrass Emma by messing about as we usually did, and to my amazement she agreed (a master stroke I'm sure you'll agree).
So I went back into the lounge and sat down to watch TV while Hilary had her bath in peace. Then after about 10 minutes I went back into the bathroom and splashed around with Hilary noisily on purpose, tickling her a bit, giving her "cleaning instructions" and generally being as embarrassing as I could. Hilary loved it.
Then she got out of the bath and wrapped herself in a towel without drying off and followed me into the lounge, where Emma was still sitting. Hilary knelt on the floor.
All clean now! I said. Squeaky clean all over, in all the little places! Oh good, Emma said, not really knowing what to say.
I then said to Hilary that towel's wet, let's hang it on the radiator. And without waiting for a reply, I bent down and gently tugged it off her so she was kneeling there completely naked. No one said anything! I put the towel on the radiator and when I turned round Hilary was lying on her tummy on a rug, watching the TV. It was a surreal situation, Emma and I dressed and Hilary lying there stark naked, all pretending to be engrossed in the TV.
Having got us into that situation I really wasn't sure what to do next, now I had got this far it all felt a bit awkward and I certainly didn't want to push it over the edge and get someone upset. So I thought well offering a cup of tea will at least enable me to shift position, so I made a cuppa for everyone and ended up kneeling on the floor beside Hilary, facing Emma, neither of whom had moved (or had said anything either). Whilst I was in the kitchen I noticed a tube of body lotion so I brought that in as well.
My next move (very risky) was to strike up a conversation with Emma (I can't remember what about) that would make her look at me and therefore at Hilary. Emma responded, probably more in rellef than anything, and as I got into the conversation I started to move my hands around (as you do) and they ended up on Hilary's backside, and eventually I was patting her backside as I was making points. By this time Hilary had joined in and by this time the three of us were gassing away as you do, except one of us was stark naked.
And then the final move was to open the body lotion and dribble it on Hilary's back, still talking all the while. Again I expected a rebuff from Hilary but there wasn't one. So then I decided to go for broke and I dripped it right down her back and the crack of her backside. I rubbed it on her back first and then I did a slow sweep downwards with the side of my hand, right between the cheeks and then back up again. I then repeated this and rubbed my hand up and down between the cheeks again as Hilary was talking quite normally about something she was going to buy.
I then touched her legs and she opened them slightly - a signal we were in there too. so I moved round and knelt down between her legs, putting them either side of me. From her position Emma couldn't see anything at all but she knew I could see everything. By this time I was confident enough to make a big thing about oiling up my hands, which made Emma laugh and then Hilary. so then I knew I was away. I oiled Hilary up like a greasy pole and then turned her over to do her front, by which time we were all laughing and joking.
Finally I told Hilary to stand up so we could have a look at my handiwork, which she did and actually she just stood there naked for about 10 minutes, chatting and moving around as if it were completely normal.
And then she put her dressing gown on and that was that. There was never any chance of a threesome, that would certainly have upset things, but having Hilary the only one naked for an hour or so was achieved. And we never did it again or actually even spoke of it again.
And by the way I had to buy a new rug as the old one was ruined by the oil.