OK, lets see if I can do this without getting carried away...LOL...
Allow me to pose a hypothetical situation:
You have known John and Jane for a couple of years now, and so far they appear to be the perfectly happy 'normal' married couple. They seem totally into each other and when in public usually can't keep their hands off each other.
One night they invite you and your wife or husband over to dinner, and you accept, having entertained them and been entertained by them on a number of occasions before. The dinner is great, lively chit chat all round, but you can't help noticing that when Jane looks at you she has a particularly sexy flash in her eyes (whether you are male or female is irrelevant, I suppose it could go either way). John on the other hand just seems to be comfortably digging the little eye games Jane is playing. Then the party moves into more comfortable surroundings like the living room. What happens next is not exactly what you had expected:
"Why don't you show them the video you took of us in Bermuda last year honey?" says Jane.
"Sounds cool" you say, always in the mood for seeing other places, especially warm ones!
As John hunts for the remote, Jane says "we were just looking at it last nite, it reminds us of so many good memories...hey John just hit play, I think I left it in the VCR".
John presses play, but instead of warm sandy beaches and palm trees, the TV screen is illuminated with the images of John and Jane gettin down and dirty, starring in a home movie of a decidely different nature.
You squirm nervously, searching for something to say, but Jane beats you to the punch. "Oh John, you naughty boy, were you watching that again? You know how that turns me on" and proceeds to plant a very long and tantalizingly intimate open mouth kiss on her hubby.
You laughingly say something to the standard effect of 'hey you two lovebirds, get a room why dontcha!"
Then they turn to you and say 'oh come on, its harmless', and then Jane says 'you know we have been so turned on by you two ever since we met you, and we've been just dying for the right time and way to somehow tell you how much we want to get kinky with you' and then proceed to describe the fantasies they've been having about 'swinging' with you and your husband or wife.
So what do you do?
Do you:
a. recoil in complete horror, stammering some excuse about the sitter needing to be home early and beat a hasty retreat for the door
b. pretend to recoil in complete horror, not wanting to reveal that you two have also had similar fleeting thoughts (but maybe you have mutual friends or something and would never want anyone to have something on you they could 'hold over' you) and leave, but on the way home wish you'd stayed
c. stay and get it on with them
d. something else (please specify)
Sooo...what would ya do?