I don't know if this counts as it was a full penetrative threesome and we did expect to have at least some level of sexual contact with a third:
Just a couple of months ago, my wife and I were out to dinner and decided to go to a strip club afterward, which is something we enjoy doing every now and then. Sometimes we just go and watch and tip girls, sometimes we get lap dances or have gone to the champagne room a couple of times in the past. It's never been anything major beyond grinding and rubbing etc., because it is one of the stricter more upscale clubs even though they can get fully nude on stage, so it is just good fun, and my wife has maintained that she is straight but just doesn't mind playing around a bit. Pretty quickly, this beautiful slender brunette caught our eye, although the decision is always my wife's, and long story short we tipped her a lot when on stage, winning her away from a bachelor party full of guys, and decided we were going to go to the champagne room with her.
Turned out she was semi new at least to this club and didn't even know how to get to the champagne room, because we were the first ones to ask her to go there, so we had to show her where it was. Once we got to the room, she says "So, they said the rules are I have to keep my panties, on but she (my wife) doesn't." Typically my wife doesn't wear them anyway and I though she wasn't, but apparently she had gone to the bathroom and put some on as the last girl we got dances from said it made it easier to play if she was wearing them.
Right away, this girl takes down the top of my wife's dress and then hikes up the bottom of it until its around her waist and slides her thong off entirely. So my one minute in and wife is just laying there, spread naked and this girl is just kneeling between her spread legs. Other girls had stripped her down in the past, but this was definitely more forward than usual.
This girl starts kissing all over her neck, then her breasts, then is working her way down her, kissing down her midsection, then moving to her legs and kissing up her thighs. I am like, wow, she is going the extra mile to tease her like she is going to actually do something... only then she didn't stop kissing up her legs.
A split second later, she leans in and starts kissing and licking my wife's clit, causing a surprised, and extremely loud moan from her and me to just look on in absolute awe. We had never done anything quite at this level with any other person ever, and my wife had never full on hooked up with any girl beyond some rubbing around and breast kissing type stuff during prior lap dances.
The girl looks up and asks if she should keep going, and we are both just like "Yes!". So this girl just dives right back in and starts eating my wife out, causing her to writhe and moan so loud I'd swear they heard her from the downstairs area. Eventually I get in on the action and, although she was rubbing, spreading and eating her, I started fingering my wife and sucking on her breasts while the dancer kept doing that.
Eventually we switched it up some and we both sucked on the stripper's breasts, my wife even felt comfortable enough to start playing with the girl's pussy as well, and made sure she danced on me for a bit, and the girl also put her pussy right on my wife's and scissor fucked her as well, but the girl kept going back to eating her out again, for minutes at a time, and then coming up for air.
I think one of the other hottest parts was when they were laying next to eachother playing with eachother after another stretch of her having gone down on my wife and then they were just full on kissing, even though my wife was literally tasting herself on the girl's lips.
About a half an hour into this though, the girl is going down on my wife again, just full on on her hands and knees with her ass in the air and the VIP hostess comes in and says she needs to talk to the girl. The girl leaves and then comes back in and sheepishly says she just got in trouble for breaking the rules (there is a camera in the room, so I wonder what took so long), and then asked ME if I knew that wasn't allowed there, as though I worked there and was going to tell her to stop. She said she just assumed since my wife didn't have to wear panties, that that would be okay.
We figured that was a good time to end it and leave. went home and had super dirty sex with tons of dirty talk about what had just happened. I did tip the girl 60% on top of the already expensive champagne room bill, I figured one for each base she took my wife to, although afterward I heard that oral sex is often considered a home run and full on sex between two girls. Afterward I heard from someone familiar with the business side of that particular club that the girl was almost certainly fired after we left.
Since that time my wife has been willing to admit maybe she isn't exactly totally straight, and when we were watching a Jimmy Carr special on Netflix, a joke of his about some women being like Spagheti: Straight until wet, sent her into a fit of laughter like he had her dead on pegged.