I once had a married woman who said she had been given a "hall pass" by her husband respond to a Craigslist casual encounters ad I had posted.Not sure if taboo, but I will bite. I want to take a lady in front of her husband and do everything he wouldn't do.
More of a fetish than taboo.
Ok, let's make it taboo.... the lady is my wife's sister.
I made it pretty clear I didn't want her husband to be there but it never panned out. Yeah, semi-regular casual sex was the big draw but I think I would be lying if I said there wasn't part of me that sort of liked that I would have been fucking a married woman and her husband would have been cool with it.