I'm not really sure this classifies as a fetish, you can decide.  Many many years ago I came up with an idea to make swinging more fun for my wife and me.  It was actually from the old porn movie Behind the Green Door that starred Marilyn Chambers.  In the movie she is a kidnapped woman forced to submit to guys who come thru a Green Door in a kind of theater where people are there to watch.  When we moved into a house with a finished basement I set part of it up as a kind of dungeon with BDSM gear.  I put up a partition wall to keep it off limits from our daughter who was very young at the time.  I would arrange for people, usually other swinger friends of ours, to visit us on party nights and I would sneak them through the garage into the dungeon thru the partition door, which I painted green as a spoof on the movie.  They would hide behind the door until I brought my wife downstairs.  The deal was my wife had to submit to anybody or anything that came into the room thru the green door.  If a guy came in with a whip she would let him whip her.  If another couple came in together she would submit to both of them.  If a guy came in with a k9 she would have to submit.  That was the idea and we did it for years, maybe three or four times a year whenever I could set up something that worked with everybody's schedules.

At a certain point our daughter was old enough to where we could not keep the dungeon secret so I decided to expand it to take up all the basement except where the boiler and laundry room was.  I made a kind of stage out of plywood and covered it with carpet, then got a king size mattress to put on top.  We already had an old sofa stored down there and I added some beanbag type chairs so we could sit an "audience" up to eight or nine people.  To make it more special I mounted a little spotlight on a beam that would shine on the green door.  We began hosting parties with bigger groups of people including friends of friends who would come for "special events."

When my daughter turned legal age she was allowed to attend our parties, of course she already knew for a long time what was going on down there.  She began to participate and now is a regular part of the scene.  We do not play favorites because of her being there, when she is part of the evenings entertainment she has to submit to whoever or whatever comes thru the green door just like her mom or any other person who is "the main attraction" that night.  I love pretending to be cucked and watching my wife and daughter being used hard and degraded.

Our parties have become pretty well known to the swinger community in our state and "underground" kinksters have come as far as 200 miles away to attend, that is as long as they are friends with one of our regulars.  We love to meet and chat with people who like what we are doing although I have to say we are extremely fussy about who we play with, also the precautions we take for bareback play, etc.  Anybody who's interested in learning more is welcome to chat with me on Yahoo Messenger.